It is important to map what is inside an area to monitor what is happening in that area and it is important to map several areas to compare these areas and what is taking place inside of the areas.
It is important to define you analysis when mapping what’s happening inside of an area. It is equally important to evaluate and consider your data/ areas and what types of features are inside the areas.
The features inside of an area can either be discrete features or continuous features. Discrete features are unique and identifiable features, you can count them or list them. You can also summarize a numeric attribute associated with them as well. Discrete features are either locations, linear features such as streams, or discrete areas such as parcels.
Continuous features represent geographic phenomena and you can summarize the features for each area. A type of continuous features is spatially continuous categories or classes. You can measure this continuous feature by finding out how much of each category or class occurs inside the area you are mapping
Another type of continuous feature is a continuous value. These are numeric values that vary continuously across a surface and can include elevation and precipitation.
The three ways of finding what is inside the area of a map are drawing areas and features, selecting the features inside the area, and overlaying the areas and features.
All three methods mentioned above are good for individual reasons when it comes to finding what is inside the area of a map.
Drawing areas and features can be done using different methods that are required for different areas such as discrete areas or continuous features
Selecting features inside an area lets you use the results as a tool for analysis such as the frequency, count, and a summary of a numeric attribute.
Overlaying areas and features lets you find which discrete features are inside certain areas and summarize them. It also allows you to calculate the amount of each continuous category or class inside areas, and summarize continuous values inside areas.
When overlaying areas with continuous categories or classes the GIS uses either a vector or raster method. The vector method is more accurate but requires more processing and the raster method is more efficient since it automatically calculates the areal extent for you but is still less accurate.
Definitions:
Frequency= the number of features with a given value, or within a range of values, inside the area, displayed as a table.
Chapter 6:
Key concepts=
This chapter is all about finding what is nearby and the purpose behind this is to find out what’s occurring within a set distance of a feature and to also find out what is within traveling range.
There are different ways of finding what’s nearby and this can be done by measuring straight-line distance, measuring distance or cost over a network, or measuring cost over a surface.
Nearby can be based on a set distance you specify, or on travel to or from a feature. Typically if travel is involved you would measure nearness by distance or travel cost
Travel costs can include things like time, money, and effort expended. These are considered travel costs because of the costs associated with each.
Taking the curvature of the earth into account is important for geodesic method and ignoring the curvature of the earth and measuring across a flat plane is called the planar method
The information needed from analysis can be summed up as a list, count, and summary. Each have their own purpose for the features that are mapped
Straight line distance is a good and simple way of finding what’s nearby, but measuring distance or cost over a network, or cost over a surface can give you more accurate measurements as to what is nearby.
Creating a buffer is important because you can use the line created by the buffer as a permanent boundary or use it temporarily to find out how much of something is inside the area. Creating a buffer is done by specifying the source feature and the buffer distance
GIS will also allow you to create buffers around multiple source features at once, and can also buffer each source differently depending on an attribute of each.
Finding individual locations near a source feature is useful if you need to know exactly how far each location is from the source instead of just figuring out if it falls within a certain distance from the source
Definitions:
Distance or cost over network= specify source locations and a distance or travel cost along each linear feature.
Cost Over a Surface= specify location of source features and travel cost, and creates a new layer showing the travel cost from each feature.
Chapter 7:
Key concepts=
This chapter was all about mapping change. Knowing what has changed can help with the analysis of the way things interact, predict future conditions, and evaluate the results of an action.
Mapping change can include showing the location and condition of features at each date, or calculate and map the difference in a value for each feature between two or more dates.
Mapping change in location can help to predict where features may move in the future
Mapping change in character or magnitude can show how the conditions in a given place have changed over time
It is important to not that change in location and change in character are not mutually exclusive
A trend is when there is a change between two or more dates and times, this typically occurs when measuring time
There are three ways to map change and these are, time series, measuring change, and tracking maps
A time series is particularly useful for showing change in character or magnitude for discrete areas and surfaces.
Measuring change is to show the amount, percentage, or rate of change in a place
A tracking map is another key concept and basically shows the position of a feature or features at several dates or times (this is good for showing incremental movement). What examples could be used with a tracking map?
The last important key concept for the chapter is measuring and mapping change. Calculating the difference in value between two dates and then mapping the value of this is how mapping/measuring change takes place. There are various data/features you can measure and map change for including discrete features, data summarized by area, continuous numeric values, and continuous categories.
Definitions:
Change in character or magnitude= how conditions in a given location change over time
Cycle= change over recurring time period
1 thought on “Week 3- Will Sturgill”
good job on this. lots and lots of stuff. hopefully, doing the tutorial (and the “final”) will show you what much of this looks like in the software and in practice and make a bit more sense.
good job on this. lots and lots of stuff. hopefully, doing the tutorial (and the “final”) will show you what much of this looks like in the software and in practice and make a bit more sense.