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

Week 6: Following Rivers Through Time

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Getting to Know Classification in ArcGIS

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 ArcGIS, Open the Louisiana Project File, and Add a New Layer

Shortcut1

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Classify Point Features by Field

1 Layer Properties The Layer Properties window 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.


  • To open the Layer Properties window for the cities layer, right-click the cities layer in the Table of Contents. Choose Properties from the menu.
    Open Properties
  • Drag the Properties window to a location where you can see both it and the map at the same time.
    08 Properties and Map

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Classify Point features by Equal Interval

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.

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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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Classify Point features by Natural Breaks

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.

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?

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 OK and close the Layer Properties window.

The histogram window for setting the breaks manually.
22 Break Values
The map results.
23 Manual Breaks


These next three images show how the types of classifications compare.
Equal Interval
25 Equal Interval
Quantile
26 Quantile
Natural Breaks
24 Natural Breaks


Movie Icon

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.

loading the player


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Classify Polygon Features by Field

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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 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.

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Classify polygon features by quantile

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.

The Parishes are now color coded by Population Density.


Movie Icon

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.

loading the player


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.

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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

  • Turn on US Rivers and Louisiana Rivers Mississippi, Atchafalaya, Pearl and Vermillion Rivers.
  • Look for relationship between rivers and settlement.
  • Answer the following questions:
    • The earliest settlements were closest to rivers, why?
    • French settlers came up from the Delta region. This map shows the early settlements in the 1700's.
      LA Historic Rivers
    • What other questions might you ask of this data?
    • How did they move inland and what crops did they grow?

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    Classify and Symbolize a Data Layer of Interest to You

    • Use classification and symbolization to illustrate a story with data.
    • Add a data layer from the Louisiana data folder, another data source, or use one of the layers already on the project.
    • Classify and symbolize the data to show an interesting pattern that was previously hidden in the data.
    • Alternately, return to the invasive species project and classify and symbolize a data set in that project.

    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

    • Explore classification of another data set.
    • Add another data layer from within the Louisiana data folder, such as Lake Ponchantrain.
    • Add another data layer from the other data folders.
    • Alternately, return to the invasive species project and classify and symbolize a data set in that project.

    Movies on this Page

    How to download movies

    • Click the link to go to the SERC media library listing for the movie. The record will open in a new window.
    • On the SERC media library page, right-click (Win) or control-click (Mac) the link (below the movie on the Flash version pages) to download the movie file to your hard drive.
    • Look below the movie window for the file download link.

      Save Movie from CMS listing

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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 ArcGIS

    Movie Icon Classifying polygon features in ArcGIS

    Movie Icon Classifying the historicsettlement layer in ArcGIS

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    iPod Versions

    Download these version to play on your iPod or iPhone.

    Movie Icon Classifying polygon features in ArcGIS

    Movie Icon Classifying polygon features in ArcGIS

    Movie Icon Classifying the historicsettlement layer in ArcGIS


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