VanderVelde – week 2

Chapter 1:

This chapter had 3 main topic, what is GIS analysis, understanding the geographic features and understanding the geographic attributes. It explained that GIS analysis is the “process for looking at geographic patterns within the data and the relationship between features.” This is done by framing the question or what information is needed. The question poised that creates the need for a map often decided how to approach the analysis. So you need to understand your data and then choose a method. From there process the data and then look at the results. This last step can help decide whether the information used is valid or whether you should return to step one and re-run the analysis with different data or a different method. For understanding the geographic features, the type of feature can affect the steps of the analysis process. The types of features are discrete, such as lines and locations that can be pinpointed. Continuous phenomena, which is like a temperature or precipitation and is given a value. Features summarized by the area are the counts/density of individual features such as population and number of things in a region. There are also 2 ways of representing geographic features, vectors and rastor. A vector model has a feature in a row on a table and the features are given a address with a x and y location in space. these features can be discrete, events lines or areas.  For a rastor model, the features are a matrix of cells in a continuous space, with each layer representing an attribute. Any type of feature can be represented using either vector or a rastor model but discrete and data summarizations by the area are usually represented through a vector model. For understanding the geographic attributes, the values need to be known. Categories, ranks, counts amounts and ratios are all attributes.  Categories group similar things together, ranks put features in order from high to low and are used when direct measures are hard or represents a combination of factors. Counts and amounts show a total number and is the actual number of features on a map. ratios shows the relationship between two qualities and rare made by dividing one quantity by another for each feature. For continuous and noncontiguous values, categories and ranks are noncontiguous while counts amounts and ratios are continuous values.

Chapter 2:

Chapter 2 focuses on why map thins, deciding what to map, how to prepare your data, making the map and how to analysis geographic patterns. Pertaining to the first question, mapping things can show you where action is needed, or what locations meet a criteria. For deciding what to map, you need to decided on what information you need for an analysis. Such as the location of the features in comparisons to a deciding factor like the example the book had, crimes compared to the police departments location. how the map will be used is also important because some features are not relevant to a topic and can muddy a maps purpose. For preparing the data, assigning geographic coordinates is something usually done via the data brought in, the same for assigning a category for the values. Making the map, there are many different types of maps, such as mapping only a single feature, such as only showing the roads or buildings. Knowing what GIS does with the locations of each feature and how it stores the location within the map. using a subset of features, this is more commonly done for individual locations. Mapping by category and displaying a feature by the type can be used. Choosing the symbiology of a map is also important as if you’re mapping individual locations using a single marker in a different color for each category of the locations can break of the map to be more legible. Changing eh locations to all have the same color but different shapes is harder to read and thus wouldn’t be recommended for this type of map. taking in to account how the map will be viewed also can help with the symbiology such as is it digital or a physical map on a poster. Analyzing geographic patterns is to ensure that the map presents the information clearly.

Chapter 3:

Chapter 3 focuses on why to map the greatest and lowest values, what needs to be mapped, how to understand the qualities within the map, creating classes, making the map with these in mind and looking for patterns. Mapping the extreme values can help people find what meets their criteria and to take action. or to see the relationships between locations. What to map is based on knowing what features you’re mapping as well as the purpose for the map. these factors will help decide how to present the features and qualities to see patterns in the map. Feature type and what is being explored within the data or presented in the map also help with what to map. Understanding the quantities of thing like counts and amounts which show total numbers are important for qualitative maps. Ratios for these maps show the relationship between two quantities and are useful when summarizing by area, with the most common ratios being averages, proportions and densities. Ranks are useful when direct measures are difficult or the quantity represents a combination of factors. Creating classes within a map groups values into their own symbols or being in the class. this requires a trade off between the presentation of the values are the generalization of said values. Mapping individual values present an accurate picture of the data when the features are not grouped together. but this requires the readers to understand more information especially if the map contains lots of values. Using the classes to group similar values features helps by assigning them the same symbol. you can do this by creating classes manually. Classes can also be created using a classes based on a larger set of features such as a population census. Making the map discusses that the GIS program gives you different options for creating your map such as graduated colors, graduated symbols, charts, contours and 3D perspectives. each have advantages and disadvantages based on the information they provide and the limitations of using such a option.  Map type is also important as it may show discrete lines or area and whether or not you have spatially continues phenomena’s that are used. Creating 3D perspectives are used most often with continuous phenomena and help viewers visualize the surface of an area such as the height and magnitude of the area. Looking for patterns helps to present that map more clearly and can be used to compare different parts of the map. The relationships between locations of features such as the highs and lows of values help understand how the phenomena behaves.

Chapter 4:

Chapter 4 features on a maps density, deciding what to map, the two ways of mapping density, mapping density for defined surfaces and creating a density surface. Map density show the highest and lowest concentrations of features and where. Deciding what to map helps to decide what method to use based on the information needed for the map. Two ways of mapping density show that you can map by defining the area or by density surface. Defined areas can be a dot or calculated a density of each surface. Density surface is usual created in GIS as a raster layer with each cell layer getting its own value providing more detailed information but requires more effort by the creator. Mapping density for defined areas, based on the two methods for mapping density. Calculation the density value for each defined areas. Creating the dot density map is a method where each area is mapped based on the total count/amount and each dot must be specified on its representation. The dots don’t represent actual locations of features. If there are individual features but want to map density summarized by defined areas, GIS can summarize features for each polygon area. Creating a density surface are raster layers that GIS calculates a density value for each cell layer.