Chapter one gives a general overview of GIS. According to the book “GIS analysis is a process for looking at geographic patterns in your data and at relationships between features.” GIS does tasks including, mapping where things are, mapping the most and least, mapping density, finding what’s inside, finding what’s nearby, and mapping change. There are different types of methods for getting the information that you need. The type of data that you work with can determine what kind of method you will want to use. Results are shown on a map, values in a table, or a chart. When you look at the results it can help you decide whether the information is valid or useful. The type of geographic features will affect the analysis process. It is important to be aware of the different types of geographic features. GIS also can measure continuous phenomena such as temperature or precipitation. Continuous data often starts out as a series of sample points. It is also important to understand different types of geographic attributes. The different types of geographic attribute values include categories, ranks, counts, amounts, and ratio. Categories help with organizing your data. Everything with the same category are alike in some way. Category values can be represented using numeric codes or texts. Ranks order the different features from high to low. Ranks are used when it is hard to use direct measurement to quantify certain things. Counts and amounts show you total numbers. They can let you see the actual value of each feature. Ratios show the relationship between two different values. For example, dividing the number of people in each tract by the number of households gives you the average number of people per household. Categories and ranks are not continuous values whereas counts, amounts, and ratios are.
Chapter two talks specifically about mapping with GIS. It is important to use maps to see where things are. When you map out where things are it can show you where action needs to be taken. For example police can use GIS to map where crimes occur each month. In order to look for geographic patterns in your data you map the features in a layer using different kinds of symbols. It is important that the map is appropriate for the audience and the issue being addressed. Maps should display detailed categorical values. Many categories are divided into subtypes. In order to create your map you need to tell the GIS which features you want displayed. You can also show them as category values. To map features as a single type you need to draw using the same symbol which might suggest differences in the features you could explore further. You can also map by using categories by using different symbols for each category value which can provide an understanding of how a place functions. For example mapping crimes by type shows you which types of crimes occur where. If you have more than seven categories you will want to group them in order to make it easier to see the patterns. Another important thing to know is that if you reassign something from one category to another it can create two different maps.
Chapter three talks about mapping the most and least. People map where the most and least are to find places that meet their criteria. Mapping features based on quantities adds an additional level of information. To map the most and least it needs to contain a quantity. You can map quantities associated with discrete features, continuous phenomena, or data summarized by area. Ratios show the relationship between two quantities and are created by dividing one quantity by another. The most common ratios are averages, proportions, and densities. Proportions show you what part of a whole each quantity represents. They are often presented as percentages. You create ratios by adding a new field to the layer’s data table and calculating the new values by dividing the two fields containing counts or amounts. There are also statistics used with GIS, specifically standard deviation. The GIS first finds the mean value by adding all data values and dividing by the number of features. It then subtracts the mean from each value to calculate the standard deviation. When making a map you’ll want to make sure it is presented as clearly as possible. You’ll want to present information that is necessary to show patterns in the data. There are advantages and disadvantages for different types of values. Contour lines can be used to show the rate of change.