Geography 291: Geospatial Analysis with Desktop GIS

Chapter 4: 

       Chapter 4 focuses on mapping density through various methods, including defining why you should map density, deciding what kind of density to map, and how to actually map density. In terms of GIS mapping, density refers to the concentration of features or values within a given unit of area/distance. A density map lets you measure designated features by concentration using a uniform aerial unit like hectares or square miles, so the concentration distribution can clearly be observed. A hectare is a metric unit of area equal to 10,000 square meters.

        When discussing why it’s important to map density, Michell gives a multitude of reasons. One being that density maps can help show you where the highest concentration of features/data is located. This makes density maps useful for observing patterns as opposed to observing individual features/locations. These maps are also useful for mapping areas that have a wide variety of sizes. For example, when mapping the number of trees within separate forests, the larger forests may appear to have more trees due to the larger area they take up. However, when mapping for the density of the trees within the forests, you may see more concentrated areas of trees within the smaller forests that are represented through density mapping. 

    As stated in previous chapters, it’s important to consider what information you want to get from the map before creating it. This will help you decide what methodology to use when creating the map. When mapping density, consider whether you want to map direct features or feature values, as the resulting maps can look very different from each other. There are two ways you can map density: mapping the density by area, or creating a density surface. You should map by defined area if you already have data that is summarized by area, or for comparing certain areas with defined borders. On the contrary, you should create a density surface if you want to see the specific analytical concentration of point/line features. Question: What do you do when a data point falls exactly on an existing defined boundary line?

Chapter 5:

         Chapter 5 discusses map/data analysis through the lens of mapping what’s inside. But what does the book mean when it says “finding what’s inside”? It is trying to say that we can identify which geographic features fall within the boundaries of other features using spatial relationships for the purpose of analysis. When in practice using real-life data, this means determining whether points, lines, and polygons are contained within a specific area. This map analysis involves monitoring what’s occurring inside a designated area, or even comparing different areas based on what they contain. In simple words, we are summarizing what’s inside an area using GIS. 

        According to the book, this can be achieved in a multitude of ways. For one, you can draw an area boundary on top of the existing features. Or you can use an existing area boundary to select and analyze the features inside it. You can even combine the area boundary and its features to create a summary of the area. Just like in previous chapters, the method you choose to use for creating your map depends on the data that is available to you and the information you are looking to gain from creating the map. When taking this into account, the type of data you have matters. For example, finding what’s inside a single area vs what’s inside multiple areas can result in different analytical findings, as you can compare multiple areas to each other for deeper data analysis.

         There are three ways of “finding what’s inside” that the book highlights, as I listed previously. In order to draw an area boundary on top of the existing features, all you really need is datasets that show the boundary of the area and the features it contains. To select for and summarize features within an area, you also need datasets that show the boundary and the features it contains, but you will also need the attributes of the features you wish to summarize available. You will need this same set of things in order to perform an overlay of areas and features.  Question: Why does it matter whether you’re working with points, lines, or polygons when figuring out what’s inside an area?

Chapter 6:

      Chapter 6 discusses how GIS mapping can be used as a tool to analyze what is nearby to an existing feature, allowing you to find out what may be occurring within a specific distance from a feature as well as monitor events within that particular feature’s range. This can be useful for various purposes. For example, finding out what’s within the traveling range of a feature can help the observer define the area that can be served by a facility. An ambulance station can do this to find out how far away possible incoming neighborhood calls are to the specific station. Being aware of what is in the traveling range of a feature can also help with designating areas for a specific use relating to the feature being observed. For example, mapping the traveling range around a lake could allow scientists to identify surrounding wetland areas suitable for conducting environmental protection.

     According to the book, you can conduct what was previously described using various methods. One being straight-line distance, in which you specify the feature being analyzed by GIS to measure the direct distance outward from that feature, thus creating an area of surrounding features within that distance. This approach is recommended when you need to create a boundary/select for features around a specific source. To perform this method, you need a layer for the source feature and a separate layer for the surrounding features. Another method you can use is measuring distance/cost over a network. This means to determine the distance or travel cost from a specific source location along a linear feature. This approach is recommended for finding what’s possible within a travel distance/cost of an area located on a fixed network like a road. To perform this method, you need the source feature location, a layer containing surrounding features, and a network layer. Please consider that each part of the network needs an attribute providing its length or cost value. These can either be created manually or chosen from a provided network. Question: Could barriers like rivers or highways affect the analysis of what is nearby to an existing feature?

 

Chapter 4

Chapter four discusses how to map density. Density shows the highest concentration of a feature. It is useful for showing patterns on a map and in areas that vary in size. Using GIS, you can either map the density of points, lines, or data from a specific area that has already been summarized. You can create a density map based on features by area or density surface. When mapping by defined area, you can map density graphically, using a dot map, or by calculating a density value for each area. A density surface is usually a raster layer in GIS. Each cell gets a density value. This method gives the most detail, but takes the most effort. Mapping density by area should be used if your data is already summarized by area, while a density surface should be used if you have individual locations, points, or lines. On a dot density map, it is common to display the dots for smaller areas, but provide the boundaries for larger areas. This keeps the data easy to read. There are four parameters that affect how the GIS calculates the density surface. The cell size determines how coarse (large cell) or smooth (small cell) the patterns appear. The search radius determines how generalized the patterns are, with a larger radius providing more generalized patterns. The GIS counts only the features within the search radius, which creates overlapping rings. When using the weighted method, it gives more importance to features closer to the center of the cell, which results in a smoother density surface. The units you choose should be appropriate for the features you are mapping. A density surface is displayed with graduated colors or contours. Graduated colors use a different shade for each value. The most common classifications are natural breaks, quantiles, equal intervals, and standard deviation.

Chapter 5

Chapter five covers mapping what’s inside to see if activity occurs in an area or summarize activity in several areas to compare them. If an activity does occur within a specific area, action needs to be taken. Through summarizing multiple areas, you can document where there is greater activity happening. You can do this by drawing an area boundary on top of the features, selecting the features inside the boundary, or combining the area boundary and features. Single areas can be a service area, a buffer that defines a distance around a feature, an administrative or natural boundary, a manually drawn area, or the result of a model. Multiple areas can be contiguous, disjunct, or nested. Discrete features are unique and identifiable, such as locations, linear features, and discrete areas. Continuous features are seamless geographic phenomena, such as spatially continuous categories and continuous values. Within an area, GIS can provide you with a list of features, the number of features, or a summary based on feature attributes. If a feature is partially outside of an area, you can choose whether to include it or not. If you need a list or count, include the partial features. If you need to know the amount of something within an area, include only features that are entirely in the area. There are three ways to find what’s inside: drawing the area and features, selecting the features inside the area, and overlaying the areas and features by creating a new layer with the GIS. Drawing should be used if you only need to see the features inside a single area, selecting is used if you need a list of features fully or partially inside the area, and overlay is good for multiple areas or if you need a list or summary of values.

Chapter 6

Chapter six discusses mapping what’s nearby so you can see what’s within a set distance or range of a feature. Finding what’s within a set distance shows the features inside an area within a set distance. Traveling range can be used to define the area served by a facility. You can measure straight line distance, measure distance or cost over a network, or measure cost over a surface. You may have the option of calculating distance assuming the earth is flat (planar method) or using a curved earth (geodesic method). Planar is used for small distances, and geodesic is used for large regions, such as a continent. Once you identify the features near a source, you get a list, count, or summary based on their attributes. You can specify a single range or multiple ranges by creating inclusive rings or distinct bands. Inclusive rings are useful for studying how the amount increases as the distance increases. Distinct bands are useful if you are comparing distance to other characteristics. Straight line distances are used to see which features are within a given distance of a feature. Creating a buffer allows you to see what’s within the distance of a source. Using selection is similar to a buffer, but the GIS doesn’t create a boundary. You can have the GIS calculate the distance between each location and the closest source, which is useful for seeing which source is closest and comparing the distance with other factors. When making the map, you can have the locations color-coded by distance or source, a spider diagram, or use graduated point symbols. Streets are common for finding what’s nearby. Each street segment is tagged with an impedance value, the most common being distance, time, and money.

Chapter 4- 

Chapter 4 highlights why density mapping is such an important GIS tool. Simply plotting locations shows where things exist, but density mapping shows where they’re actually concentrated and where they thin out. Looking at values per unit area makes spatial patterns much easier to notice and compare across a region.

One thing the chapter makes clear is that there isn’t just one way to map density. In some cases, using predefined boundaries like counties or census tracts works best. This approach calculates density within each area and usually shows up as shaded polygons. It’s helpful for comparing regions, but it can also be limiting since internal variation gets hidden by those boundaries.

Another option is density surface mapping, which creates a continuous surface instead of sticking to fixed borders. Density values are calculated for each raster cell based on nearby features within a chosen distance. These maps are better at showing gradual changes and identifying hotspots, which makes them feel more realistic. At the same time, they take more processing power and require more careful decisions.

Chapter 5- 

Chapter 5 is all about answering the question of what is actually inside something else. Instead of just mapping layers and looking at them separately, this chapter explains how GIS can be used to figure out which features fall within certain boundaries. It feels like one of the most useful parts of GIS because it connects maps directly to real questions.

A big idea in this chapter is spatial overlay. This is when different data layers are stacked on top of each other to see how they interact. Depending on the tool you use, such as intersect or union, you end up with different results and keep different pieces of information.

The chapter also talks a lot about containment, which is figuring out whether points, lines, or polygons fall inside another feature. It sounds simple, but it becomes really powerful when applied to real situations. Things like counting how many schools are within a certain area or identifying neighborhoods located in an environmental risk zone feel very doable using GIS.

Something that stood out to me is how careful you have to be with your data. If layers do not line up correctly or boundaries are inaccurate, the results can easily be off. The chapter makes it clear that GIS is not automatic or perfect and that users still need to think critically. Overall, Chapter 5 makes GIS feel more relevant and useful.

Chapter 6- 

Chapter 6 focuses on figuring out what is nearby and why distance matters in GIS. Instead of just asking what is inside certain boundaries, this chapter looks at how close things are to each other and how that closeness can affect analysis. This feels useful because so many questions depend on distance, like access to services or exposure to certain conditions.

The chapter talks a lot about proximity analysis, which is used to measure distance between features. One common method is creating buffers around points, lines, or areas to see what falls within a certain distance. Buffers make it easier to answer questions like which schools are within a mile of a park or which homes are close to a major road. I liked how this made distance feel more concrete instead of abstract.

Another important idea in this chapter is choosing how distance is measured. Distance can be straight line or based on actual travel paths like roads or sidewalks. The chapter points out that this choice can change results a lot, which made me realize how important it is to think about what “nearby” really means in each situation.

Chapter4-Chapter 4 talks about the importance of using. Density maps: how they’re used, what they should be used for, and how the GIS System is used to make these kinds of maps. With your data, you can decide what kind of way you want to map out density. It tells you exactly which density map to use. Is specifically why you should use them. The two ways you can map out density are defined area and density surface. Both use completely different ways of mapping density and have many benefits and some downsides. When mapping by a defined area, you are either using mapping dots or calculating the Density value for each area. Using dot density mapping, maps show density graphically rather than the density value. A density surface is usually created in the GIS as a raster layer. This approach provides the most detailed information but requires more effort. When using a density surface, you usually use colored layers to indicate how Many of one thing are in that area. When using it, use specific colors to better interpret the dot-density map. It is important that you don’t make your dots either too big or too small or place them in a way that makes the pattern unrecognizable. If you do this, it might be very hard for a person to understand your map and the main points you are trying to highlight. Make sure to always double-check your units because this may affect how your map is displayed and the information on it. If you are using. If you have a density layer map and use a different unit, it may calculate and display your information differently from how you want. 

 

Chapter 5- When trying to figure out what’s inside your map, an important thing the chapter says is that you might want to circle the area that you are trying to understand. When trying to figure out what is in your area, there are many ways to do so, and the methods you use depend on the information and data you have. Ways that may determine your data include whether you are looking into multiple areas or one specific area. If you are looking to explore multiple areas, show how much of something is in each area. If you’re looking at multiple areas, you’ll want to be able to identify each area by name. If you, for example, were using fire stations across multiple areas, you might want to list each fire station as fire station alpha, fire station delta. It lets you compare the areas together. If you’re looking at a single area, you can monitor and summarize information about it. When looking at features inside an area, can we list them as discrete or continuous?  Discrete features are unique to that area. Count them or put a numeric value on them. Continuous features represent seamless geographic phenomena. When reviewing your Analysis, you will need to determine whether to list, count, or summarize all your attributes. You can choose to include only features that fall completely inside, features that fall inside but extend beyond the boundary, or include only the portion of the features that falls inside the area boundary. When trying to find what’s inside an area, there are multiple ways to draw the area and its features, select the features within the area, and overlay the area and its features. Each of these has its own benefits and trade-offs. Drawing areas and features helps figure out whether things are inside or outside an area. The trade-off is that it is quick and easy, but it’s only visual. A summary of what’s directly inside the area. The trade-off is that it is good for getting information within a single specific area. Overlaying the areas and features. Identify the features within multiple areas and summarize them by area. The tradeoff is More time consuming and requires more processing from GIS

 

Chapter 6: When trying to figure out where something is in relation to something else in GIS, we will have to decide whether to measure it by distance or cost. Distance is one way to define and measure how close something is. The other would be by the coast, depending on how long it would take to get there. Once you find nearby items by distance or cost, you will need to determine how many items to list, count, or summarize that are near what you are measuring. When looking for this, a thing that might be Inclusive rings. Which rings would help you find what’s in the distance or within your budget? Another helpful kind of ring is a Distinct band. These bands are useful for comparing distance with other characteristics. Whenever you’re trying to figure out what’s inside, there are many different ways to determine the distance between each thing. There are three ways to determine whether they are straight-line distance, distance, or cost over a network, or cost over a surface. For using the straight line distance. Its prose is relatively quick and easy, and it measures distance. The cons of it. It only gives you a rough approximation of travel distance. When using distance or cost over a network, it measures the distance or cost. It gives a more precise travel distance. But the downside is that it requires an accurate network layer, which can be challenging. Cost over a surface measures cost. Its prose lets you continue combining several layers to measure the overall travel cost. It requires some data preparation to build a cost surface, which may cost you extra time. After determining which one you’ll use, you’ll have to create a buffer. Buffers draw lines around a feature at a specific distance. 

CH 4-

Chapter four of the book goes over density in relation to GIS mapping; its uses, formats, and when it’s a good choice to utilize. Density mapping can be a great tool when graphing visuals on populations of various things (i.e., people, businesses, animals, plants, etc.). It can be done by a defined area or by loose markings, which can in turn be symbolized by shading or pinpoint markers. The style chosen is based on the information you are trying to represent. If you are mapping population by county of a certain state, defined barriers would work well. However, if you are attempting to establish a coffee shop in a town, pinpoint markers would be best.

CH 5-

Chapter five goes over “mapping what’s inside”, where information is mapped within a certain defined area, either for data on that region or for comparing regions to one another. This form of mapping focused on one area, but on many things within that area. Chapter five also goes over the type of information and analysis needed, depending on the goal of mapping. For example, do you want everything outside of your desires mapping area to be shown with only the desired area highlighted, or do you want only information to be shown within the desired region? This is once again dependent on the intention of the map. It also goes into how to decide what features to show on your map; are roads important features? rivers?

CH 6-

Chapter six talks about distance and how far out to map from your desired location. It also speaks on what specific features outside of your zone to focus on, depending on the map’s intent. The unit of “distance” you use is also an important factor to weigh in. For something within the natural sciences, this distance can be “meters from a water source”, but for something more anthropocentric, distance might be better measured as “walking time from campus”.

 

Chapter 4:

This chapter focuses on mapping density as a way to move beyond where things are to populations. Instead of counting features per location, density maps show how concentrated those features are across space, which is often more useful for understanding patterns and making decisions. Mitchell walks through two main approaches: calculating density for predefined areas (like people per square mile) and creating a continuous density surface from point data. He emphasizes how choices like area size, classification method, and search radius affect the patterns you see and the story the map tells. The chapter also ties density mapping to practical questions like identifying hotspots, comparing demand across regions, or planning services based on intensity rather than raw counts. Overall, it frames density as a way to reveal underlying structure that other maps might miss. Most of this chapter seemed fairly straight forward like the density when looking at a map. I feel like when you are given a key for a map it is hard to misinterpret density. However, some points made by Mitchell made me think a little. For example, the search radius and how much area a spot represents on a map. This is important to know and I didn’t previously think a about it. A term used a lot in the chapter was density surface. I learned that density surface is basically just a smooth map that shows concentration smoothly on a map rather than just points. Overall, I found the chapter pretty interesting because I was familiar with most of it but also learned a few new things.

Chapter 5:

This chapter focuses on using GIS to figure out what features or values exist inside a given area. Mitchell frames this as a basic but essential spatial analysis . Once you define a boundary like a neighborhood, watershed, service zone, or habitat you often need to know what’s contained within it. The chapter walks through several approaches, starting with simple counting and moving to summarizing attributes, such as total population, average income, or total length of roads within an area. He also covers how to handle situations where features only partially fall inside a boundary, which leads to splitting features and proportionally allocating values. Throughout, the emphasis is on using these techniques to support real decisions, like estimating demand, assessing environmental impact, or comparing regions fairly. Overall, the chapter shows how the what’s inside analysis turns data into meaningful, area‑based summaries that help interpret what is really going on in that area. I think of this chapter as just taking a deeper look into points. Something that I previously did not think about was the idea of handling features that are only partially inside of a region. Mitchell says that you can cut the area to better fit a split region or allocate it. The chapter also shows real world ways GIS and taking a deeper look can be useful. Things like estimating population inside a hazard zone, calculating how much habitat falls inside a proposed development, figuring out how many customers live inside a store’s trade area, or measuring road miles inside a district.

Chapter 6:

This chapter focuses on how GIS helps you analyze proximity, which is one of the most common spatial questions. Mitchell breaks this into several techniques. The simplest is identifying features within a set distance, like schools within a mile of a highway or wells near a contamination site. He then expands to buffering, where you create zones around points, lines, or areas to see what falls inside those zones. The chapter also covers measuring actual distance rather than straight‑line distance, which matters when movement follows roads, rivers, or terrain. Mitchell shows how proximity analysis can compare distances between features, rank locations by closeness, or find the nearest facility. The chapter emphasizes that proximity isn’t just about distance and that its more about understanding how closeness influences interaction, accessibility, and potential impact. Something I found interesting in this chapter was the inclusive rings and the distinct bands. These tools make it easy to find how many points, like customers for example, are within a circle of a given radius. You can also seem how that number changes as you increase or decrease the size of the radius. Another thing I saw that would have many real world applications is the distance or cost over a distance. I can see how this would be used in GPS for maybe emergency vehicles and others. Another interesting thing in the chapter was using distance as a proxy. You could measure distances of households from a store to project sales. I also thought that how you could create a distance surface in maps was cool. Overall, I thought the chapter was decently straight forward but interesting seeing all the different maps you can create using distances and its many applications.

 

Chapter IV

 

Chapter four is entirely focused on density based mapping. At first I believed this chapter was going to feel like a tedious slog, given that density based maps do away with precise location in favor of a more relative form (such as population per square mile). Effectively mapping density is a trade off from point based data to quantitative data which I believe to be somewhat redundant given that point based data typically tend to show density anyways.

However, upon reading the chapter I do believe that density mapping has its uses, especially when cross examined with more point driven data. An example the textbook gave for this was comparing sights of crimes with regional information on average income in the areas or reported gang activity. 

The GIS software does plenty of work as far as plotting and interpreting the density based data goes, including totalling the number of values within a designated area and dividing it equally across the size of the area in question as well as both general averages of the data and weighted averages.

Much of the general advice from the previous chapters apply here as well. One which I feel is a little bit redundant at this point is the specification on the classes of value a density map should have to be easily readable. This is something that was discussed in the previous chapters relative to the different classes of point based data. (More point classes makes the map harder to read, applies the same to value classes in density mapping)

 

Chapter V

 

Finally I am getting to exciting things! Mapping within a certain radius and interpreting data within that is the kind of geographical analysis I took this class to learn about.

The chapter designated several types of area based maps: Single areas (Within a single area, it is in the name) Buffers (an area surrounding a certain feature or features) and boundaries. (the boring one)

There is also a distinction to be made between the maps I just discussed and mapping multiple areas, such as contiguous areas which typically are located right next to each other, and Disjunct areas which have “buffer land”.

Then the chapter discusses discrete and continuous features. We have been over this.

The GIS software is capable of several methods of analyzing limited maps. The book has the example of a flood map and shows the GIS being able to find specific designated areas that may fall within or without the flood path, as well as being able to count and/or list the designated areas within the flood path. There is even the ability to create distinctions between the areas and categorize them by value or type based on whether they fall within the designated focus area or create visual data representations based on the data within the areas.

 

Chapter VI

 

I feel the subject matter of this chapter overlaps considerably with the previous chapter. Once again, this is based nearly entirely on mapping within a certain area. The primary difference being the discussions on how the GIS software can calculate the distance (or cost) and possible travel routes. 

Of course, nothing fun is ever easy and frankly a wrench was thrown into my ideas on applying this when the book discussed the differences between miles based on a certain geographical projection (effectively assuming the earth is flat) and based on the curvature of the earth. I hope the difference between these values will not be too big of an issue given the rather limited area I intend to map, but I know for a fact if I were mapping a larger scale project that this would potentially derail my analysis completely. 

The book describes the differences between different methods of mapping using proximity as the primary considerations as well as discussing the measure these methods record and which situations these can be applied in.

I actually really enjoyed reading about the cost over surface method. I am currently reading about the construction of the first trans-continental railroad which used a great deal of cost over surface mapping when surveying the land and even using that to modify the land to be better suited for rail transportation. (The TV show Hell on Wheels famously depicts a “cut crew” who would dig up large amounts of earth to construct a level railbed.)

This leads into the next thing I thought was interesting: Networks. Using lines that can represent road, railroads, or airways the GIS can automatically calculate the distance or cost by only following the network to the intended destination. I feel like that is one of those things that is so obvious to the common man that it effectively vanishes from our consciousness.

Chapter 4: 

Chapter Four’s focus is on density mapping, which is a way to understand how specific features or events are distributed across space. Rather than simply showing where things are located, density mapping highlights the concentrations, variations, and spatial relationships within data. By calculating the values per unit area, density maps allow users to see where features are clustered, sparse, or unusually high or low, which adds important context that simple point maps cannot provide. 

The chapter explains that there are two main approaches to mapping density. The first is mapping density within defined areas, such as counties. This method relies on existing boundaries and calculates density by dividing the number of features by the area of each region. These maps are often displayed using shaded polygons and are useful for comparing one area to another.

The second approach is density surface mapping, which produces a continuous surface using raster data. Instead of fixed boundaries, density values are calculated for each cell based on nearby features within a given radius. This method is more detailed and visually expressive, making it better suited for identifying spatial patterns, gradients, and hotspots. However, it also requires more processing time, storage, and careful design choices on the users end. Before creating a density map, the user must decide what they want to analyze such as raw counts, normalized values, or interpolated surfaces. Raw counts will show simple distributions, normalized values will allow fair comparisons across areas of different sizes, and interpolated surfaces will reveal patterns and relationships. The chapter also discusses practical GIS considerations to take into account, such as choosing cell sizes, classification methods, and effective color schemes to represent the data.

Overall, the chapter demonstrates how density mapping can be applied across many fields from environmental science and public health to business and urban planning by clearly showing how values vary across a region and where concentrations are highest or lowest.

 

Chapter 5: 

Chapter Five shifts the focus of GIS analysis from broad spatial patterns to narrowing in on specific areas and features. Rather than viewing the entire dataset at once this chapter emphasizes how GIS can be used to isolate only the information that is relevant to a particular research question. This targeted approach will allow users to answer questions about what exists within a defined boundary by making spatial analysis more precise and meaningful. A major theme of the chapter is the importance of clearly defining the area of interest before beginning any sort of analysis. GIS provides several ways to make these boundaries, including service areas around facilities, buffers that represent distance limits, and natural or administrative boundaries such as watersheds or political regions. You may work with a single area or multiple areas, which can be contiguous, disjointed, or nested. Choosing the correct type of boundary depends on both the question and the nature of the data being examined.

The chapter outlines three primary methods for determining what lies within an area. The first involves manually drawing areas or features, which can be useful for quick visual checks but may lack some precision. The second method uses GIS tools to automatically select features that fall within a specified boundary, producing more accurate lists or summaries of those features. The third and most powerful method is overlay analysis, where layers are combined so their attributes intersect. This approach allows users to calculate how much of a feature exists within an area or to create new datasets that merge information from multiple layers.

Chapter Five also revisits the distinction between discrete and continuous data, reminding us that feature type plays a key role in selecting the appropriate analytical methods. This chapter highlights how effective GIS analysis depends not just on technical tools, but on thoughtful decision making about data types, boundaries, and analytical goals to accurately represent your data. 

 

Chapter 6: 

Chapter Six focuses on the concept of proximity which involves determining what is close to a particular location or feature. Proximity analysis is essential in many real world situations because distance strongly influences access, risk, and decision making. Whether planners are deciding where to locate public facilities or scientists are studying environmental impacts, understanding what is nearby provides critical insight. The chapter emphasizes that proximity analysis must begin with careful definition. Analysts must decide what “near” actually means in the context of their study and how it should be measured. GIS offers several ways to do this, each suited to their different situations. 

The most basic method is straight-line distance, which measures the shortest path between two locations. This method is simple and useful for creating boundaries, it does not account for realworld obstacles such as roads, rivers, or terrain. To address these limitations, the chapter introduces network based distance or cost, which measures travel along actual paths like streets or sidewalks. This method is commonly used in navigation systems and is more realistic when movement is restricted to established routes. A third approach, cost over a surface, incorporates barriers and varying levels of difficulty across a landscape. This method is particularly valuable in environmental and ecological studies where movement is affected by natural features. The chapter also explains how proximity can be measured across the Earth’s surface using either a flat plane approach for small areas or a geodesic approach for larger regions. In addition to this proximity ranges can be specified using inclusive rings, which show how effects accumulate over distance, or distinct bands, which allow comparisons between distance zones.

Chapter Six demonstrates how GIS based proximity analysis accurately helps translate spatial data into practical information. By selecting appropriate distance measures and methods, we can better understand how an event or data can affect its surrounding area, allowing for more accurate data representation in our maps. 

 

Chapter 4

 

Chapter Four is all about mapping density, in other words, looking at how particular criteria are disturbed. Density doesn’t just show us locations of the criteria we are searching, but instead helps us see concentration and relationships among the data. We are able to find per unit area with density. This helps in many different fields and areas. There are two ways to approach density maps. The first way looks at density in defined areas. Existing boundaries are used to calculate how many of a particular criteria fall in a particular square mile. Maps of this nature are displayed with shaded areas. The other method is density surface mapping. Continuous areas can be used for this instead of predefined boundaries. The raster type layering is used for these maps. This helps show patterns as well. When using density mapping you first have to decide if you are looking at how many, called raw counts, unit area amounts, called normalized values, or density gradients, called interpolated surfaces. If you want a simple distribution, use raw counts. If you want to make comparisons, use normalized values, and if you want to see patterns, use interpolated surfaces. I like that density mapping is more than just seeing dots on a map. We can see where things occur the most and when they thin out. We can also easily see outliers. This all helps to add context to points. For another class I have selected a project idea about hellbenders and the effect the PFAs have on them. I would use density mapping to determine where populations of hellbenders are highest and lowest. I would do the same for PFA levels. These layers together would help me draw relationships and make educated guesses about the effects of PFAs on the hellbender population. My point is, this can be used to make sorts of comparisons and relationships. 

 

Chapter 5

 

Chapter Five is focused on isolating the relevant data needed, instead of looking at the big picture. GIS helps isolate the features and boundaries that the researcher is interested in looking into and filters out the rest. There are three methods to use to do this. The first method is drawing areas and features by using either the boundaries already existing in the software or creating new ones to look at the area of interest. This method is limited however because manual drawing can be less precise. The second method is selecting features within an area. This has more precision. The program selects features inside specific boundaries. The last method is using overlaying areas and features where layers are stacked so that datasets intersect. This chapter helps pull some of the broad concepts of earlier chapters together and focuses on methods using spatial reasoning. This chapter helped to understand more of the “science” behind mapping. I like that in each chapter there are multiple methods to do things and the book helps outline the reasoning behind choosing one over the other. This brings back the point from earlier chapters, where the researcher needs to know what they are looking for and how they want to convey that message, in order to choose the correct method. This chapter also reviews the idea of discrete vs continuous data. This is important to remember when selecting methodology, and I like that the chapter did a reminder of that. 

 

Chapter Six

 

Chapter six focuses on the concept of proximity. This means finding what is nearby a particular place or feature. Proximity is important in real-world applications. Distance plays a role in assessing risks, distribution of goods, and access to different things. For example, if you are planning a park, you may need to map how close the park is to a school or other parks in order to determine if a park is needed or if there are likely to be people to go to a park. You also wouldn’t want to put a park next to a prison. So looking at proximity to different features is really important. Just like in previous chapters, this chapter mentions that it is important to define what you are looking for, before you begin. The proximity question starts with defining. You need to define what nearby means, what metrics are you using? One way to find nearby is to use the straight line distance. This is measurement of a direct like between two features. This is simple, but doesn’t account for obstacles in the way. My mom would call this “straight as the crow flies” measurement. We have all been told that something is just a mile down the road, but it took 10 minutes to drive there due to stop lights and cross walks, and having to keep the car on the road. None of those things are accounted for in the straight-line method. A second method is measuring distance or cost over a network. Network distance is more meaningful when a straight path can’t be taken. This accounts for the time and distance along actual paths. This is what you get when you put your destination into Google Maps. Lastly, there is the calculated cost across a geographic surface. This takes barriers into account. Environmental analysis uses this method. It is important to account for the method needed for what you are analyzing. If we think back to the park example, if there is a river running through town and a railroad track, there are barriers to kids accessing the park. You can’t just pick a point and assume that everyone has access that is inside that circle of proximity.

 

 

Chapter 4:

This chapter shows us how to map densities using the GIS, and why this can be useful to many people, from business owners to the average person looking to find out what’s within 1,000 feet of them. To put it simply, mapping densities shows you exactly how values vary across a region as well as where the highest/lowest concentration of a feature is. It is very useful in analyzing patterns and measuring the number of features using a uniform area unit such as square miles or hectares. A common use for density mapping is census tracking of population densities. Other common uses include locations of different businesses, and the number of employees in each business.

There are 2 common ways of mapping densities;

By defined area: This method is typically used if you want to compare areas with defined borders. It can be done with geographic mapping, dot mapping or by calculating a density value for each location. Dot maps are usually used to represent individual locations (eg. trees) and density values can be calculated by dividing the total number of features by the area of the polygon.

By density surface: A density surface is typically created by the GIS as a raster layer. Each cell in the layer is a density value (eg. no. of businesses within a square mile) based on the number of features within the radius of the cell. This provides very detailed information, but requires a lot of time, effort and storage. This method can be useful if you have individual locations, sample points or lines. One practical bit of advice in regards to this method was that you can use the GIS to change the sizes of the dots based on their densities in a map.

The chapter also goes over how you can use the GIS to create a density surface; convert density units into cell units, divide this value by the number of cells and take the square root of this value to get the cell size. It also gives more information about different data categories (eg. natural breaks, standard deviation) and gives advice on how best to use colors and contours to display your data. Overall, I think the chapter explained the process and intricacies of mapping densities in GIS very well. It did make me wonder if the mapping process changes when you are mapping over different surfaces, eg. land and water.

 

---

Chapter 5:

This chapter focuses on mapping what is within a certain region or border. People can want to do this for many reasons, but one of the more common ones is to compare different areas based on what is within them, eg. monitoring drug arrests within 1,000 feet from a school.

One of the key steps in this process is defining your analysis. To do this with the GIS, you must draw an area boundary on top of the features and use the boundary to select the features within it and list/summarize them. The area boundary and feature data can also be combined to create summarized data. In order to effectively carry this out in GIS, you need to consider 1) how many areas you have at your disposal and 2) what types of features are inside the area. One type of area boundary is a single area. Types of service areas include;

• A service area around a central facility (eg. a library district)
• A buffer that defines a distance around some features (eg. a stream off limits to logging)
• An administrative/natural boundary

You could also choose to work with multiple areas. Types of these include;

• Contiguous (eg. zip codes, watersheds)
• Disjuncts (eg. state parks)
• Nested (eg. 50- and 100- year floodplains)

Similarly to previous chapters, chapter 5 also briefly touches on the different kinds of features; discrete features (unique, identifiable features such as student addresses or locations of eagle nests) and continuous features (features that represent seamless geographic phenomena). I found this section to be very useful because it reminded me of the different feature types you can deal with in GIS, and encouraged me to do my own research into how they can appear and be displayed in GIS.

Finally, the chapter covers the three ways of finding what is inside:

• Drawing areas and features: You can use the GIS to create maps to see whether one or a few features are inside or outside a boundary
• Selecting the features within the area: Specifying the area and layer containing the features you want can help you get a list of features within one or multiple groups.
• Overlaying the areas and features: Combining the area and features to create a new layer with attributes of both can help you find out how much of a specific feature is in one or more area

---

Chapter 6:

This chapter went over how you can utilize GIS to find out what is nearby you or another location altogether. Finding what is within a set distance can help identify an area, as well as the features inside the area that have been affected by an event or activity. One example of the GIS being used in this way is notifying residents within 1,000 feet of an accident. It can also be used to define the area served by a facility (eg. a library) and delineate areas suitable for a specific purpose. One example of this would be a wildlife biologist mapping an area within a half mile of a stream.

The textbook states that in order to find what is inside a set distance, we need to define and measure the concept of “near”. It can be defined by a set distance or the travel to/from a feature. And it can be measured by distance and cost. When analyzing the surface of the earth, we can either look at it with the flat plane method (typically used with small areas of interest) or the geodesic method (normally used with larger areas of interest such as continents). We also got an explanation of the 2 ways we can specify a range; inclusive rings (useful in finding out how total amounts increase as distances increase) and distinct bands (useful in comparing distances to other characteristics, such as the number of customers within a 1000 vs 2000 year range).

And finally, in the section I thought was the most interesting, the textbook covers the 3 ways of finding out what is nearby;

• Straight-line distance: By specifying the source feature and the distance, the GIS can find the area or the surrounding features within the distance. This method can be good for creating a boundary.
• Distance/cost over a network: Specifying the source locations and a distance/travel cost along a linear feature can help you find what is within a travel distance/cost of a certain location.
• Cost over a surface: Specifies locations of source features and a travel cost.

Overall I thought this chapter was intriguing because of how relatable it is to the lives of many people. The average person on most days most likely uses GPS technology everyday to find locations nearby them (eg. supermarkets, restaurants) to learn more about what is in their area. The information in this chapter can also be useful to those who wish to conduct scientific research and analyze data (eg. a wildlife conservationists who want to look at residential areas near a riverbank). This chapter also made me anticipate working with the GIS software later in the semester and doing my own investigations with the data provided.