Eyes in the Sky II > GIT Web Course > Module 2 > Week 6 > Getting to Know Classification > Getting to Know Classification in AEJEE

Week 6: Following Rivers Through Time

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Getting to Know Classification in AEJEE

So far the information displayed on the Louisiana GIS map gives you a good overview of where the Cities and Parishes in Louisiana are located. However, in order to communicate more in-depth information about the map's features we are going to modify the map symbols to not only show location, but also to display additional information about the data they represent, such as numbers of homes or population. This type of representation of data is known as classification.

Launch AEJEE, Open the Louisiana Project File, and Add a New Layer

AEJEE_logo

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Classify Point Features by Field

properties cities The Properties window in AEJEE.

Open the Properties window for the cities layer by right-clicking (Win) or control-clicking (Mac) the cities label in the Table of Contents.

Choose Properties from the menu. Then move the Properties window so you can see both it and the map at the same time.


  • To open the Properties window for the cities layer, right-click (Win) or control-click (Mac) the cities label in the Table of Contents. Choose Properties from the menu.
    right click to open prop window
  • Drag the Properties window to a location where you can see both it and the map at the same time.
    2. prop window open

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Classify Point features by Equal Interval

In the Properties window for the cities layer, graduate the size of the symbols to emphasize the Population of 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.

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Classify Point features by Quantile

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:

Thought question:
How do you think Quantile classification breaks up the data?

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Compare the difference in these two methods of classification

Equal interval classification breaks up the population data into groups having an equal range of values (i.e. 0-10, 11-20, 21-30, etc.). In this case, when Louisiana cities are mapped by equal interval, it highlights the fact that most of the cities have low population.

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.

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Manual Classification of Point Features

In these first two types of classification, the data are 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.

Use the equation (POP_90 >= 219531).
The result is two cities: Baton Rouge and New Orleans.

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?

Perhaps, rather than letting AEJEE choose where to set the classification breaks using the Equal Interval or Quantile methods, you want to set your own intervals. This is called Manual Classification.

To set Manual breaks:

  1. The Properties window for the cities layer should be open. If not, right-click the cities layer in the Table of Contents and choose Properties from the contextual menu. If necessary, click the Symbols tab.
  2. Set Draw features using to Graduated Symbols and the Field to POP_90. The number of classes should be 5.
  3. In the Classified by popup menu, first choose Quantile to reset the class breaks (these instructions won't work if you switch from Equal Interval to Manual), then choose Manual. The Set Class Breaks and Histogram window will open.
  4. In the Set Class Breaks and Histogram window, click the Select Break menu to see the current classification breaks.
    You can't change the upper and lower numbers in the Select Break menuthey're the minimum and maximum values in the Pop_90 field. You also can't change the break points to values that are less than the next lower break point or more than the next higher break point. This makes the process a little tricky to learn. For now, just follow these directions exactly.
  5. In the Select Break menu, select the last break just above the maximum (probably 6259). In the Current box, change it to 220000 (commas are optional).
  6. Select the next highest break point (probably 2720) in the Select Break menu and change it to 100000 in the Current box.
  7. Change the next two breaks to 40000 and 10000, respectively.
  8. Close the Properties window.

(Disclaimer: If you are finding Manual Classification difficult, just skip this step and look at the pictures below.

This is the histogram window for setting the breaks manually.
setting breaks
This is what the map looks like after symbolization using Natural Breaks.
map and manual

These next three images show how the types of classifications compare.

Equal Interval
comparing classification 1
Quantile
comparing classification 2
Natural Breaks
comparing classification 3


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Classify Polygon Features by Field

Classify polygon features by unique value

It is also possible to classify polygons in order to display a variety of information. Previously, you investigated the data in the attribute table. Classification allows you to select and display that information on the map.

While still in the Properties window, click on the symbol next to the value you are symbolizing. This will bring up a color picker window. From the Swatches window, you can change the color of any of the fills.

Another method to choose a color palette is to use the Color Scheme pull down menu and choose a different palette of colors, such as minerals or pastels. 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.

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Classify polygon features by quantile

Just like with 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.

The Parishes are now color coded by Population Density.


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Observe the relationship between the cities layer and the Parishes layer. It comes as no surprise that the Parishes with the largest cities also have the highest population density.

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Add Historic Settlement Patterns and Rivers to Discover the Relationship between People and Rivers

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.

Now let's explore the question, "How was the State of Louisiana populated over time?"

Symbolize the historicsettlement layer


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Classify and Symbolize a Data Layer of Interest to You

This is the screenshot that you will post to your discussion group for your required weekly assignment.

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Explore More if you have Time

Movies on this Page

How to download movies

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Flash Video Versions

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.

Movie Icon Classifying point features in AEJEE

Movie Icon Classifying polygon features in AEJEE

Movie Icon Classifying the historicsettlement layer in AEJEE

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iPod Versions

Download these version to play on your iPod or iPhone.

Movie Icon Classifying polygon features in AEJEE

Movie Icon Classifying polygon features in AEJEE

Movie Icon Classifying the historicsettlement layer in AEJEE


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