Getting to Know Classification in ArcGIS

Open the Layer Properties window for the cities layer by right-clicking the cities layer in the Table of Contents. Choose Properties from the context menu. Then move the Layer Properties window so you can see both it and the map at the same time. In the Properties window for the cities layer, graduate the color of the symbols to emphasize the Populationof Louisiana cities in the year 1990. Select the following options: Thought question: Study the map - How do you think equal interval classification breaks up the data? The map now displays the location and population of each city in Louisiana. The data is differentiated both by size and color. It is split into 5 groups with the cities that have the largest population colored with red dots. However, the data on the map is hard to interpret. Notice that all the cities are almost all of one size. Return to the Properties window and adjust your settings. There are other ways to break data sets into groups. Try separating the population data into quantiles. In the Properties window, select the following options: Quantile classification on the other hand, breaks up the data into groups having the same number of features (i.e. 10 per group, 50 per group, etc.). However, this type of classification can be misleading. In these first two types of classification, the data is not represented in a way that helps reveal patterns on the map. Why, you might wonder? Carry out a query to do a little more investigation of the data. Set up a query that asks how many cities in Louisiana have a population greater than 220,000. Make queries for these other questions: How many cities have a population between 220,000 and 100,000? How many cities have a population between 100,000 and 40,000? How many cities have a population between 40,000 and 10,000? How many cites have a population less than 10,000? Take another look at the Attribute table for the data and observe the patterns in the data. Before setting up a third type of classification, Natural Breaks. Note: We are going to do this manually. To set Manual breaks - In the Classification window choose Manual, in the Breaks Values window, select the first break, 10000. In the next break type 40000 to reflect the next break change the next level to 100000. Repeat this procedure for all of the five breaks listed below. (Disclaimer: this can be a bit hard to accomplish, so if you are finding this difficult, just skip this step and look at the pictures, below.) Click on the movie to open up the movie in the SERC Media library. Then click its name to play it. Close the window when you are done. While still in the Properties window, click on symbol next to the value you are symbolizing, this will bring up a color picker window. From the Swatches window you can change the colors of any of the fill values. Another method to choose a color palette is to use the Color Ramp pull down menu and choose a different palette of colors, such as minerals or pastels. If you want to see the word descriptions of the Color Ramps, right click on the color bar and uncheck the Graphic View.Explore these other options on the map. When working with multiple layers, the Transparent color fill can be useful. This allows the map to show boundaries of a polygon, as well as the data layer below it on the map. For example, if you had an image layer such as a NEO land surface temperature image and you wanted to overlay political boundaries over that image, this would be the technique that you might use. Just like in point layers, it is possible to display multiple types of information on the map by classifying the polygon layers. To illustrate this idea, change the classification of the Parishes layer to display information about Population density. Click on the movie to open up the movie in the SERC Media library. Then click its name to play it. Close the window when you are done. Observe the relationship between the cities layer and the Louisiana Parishes layer. It comes as no surprise that the Parishes with the largest cities also have the highest population density. Up to this point, you have captured one year's worth information on the map and with that year's data told a story about the population of Louisiana in 1990. However, maps can tell stories that explore both spatial and temporal questions. This is the screenshot that you will post to your discussion group for your required weekly assignment. Download these versions to play on your computer. You'll need an appropriate movie player to view the file, such as Flash Player, Real Player (Mac / Win), or Adobe Media Player. Source.


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Last Modified: April 18, 2016 @ 11:11 am