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

Week 6: Following Rivers Through Time

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Getting to Know Classification in My World

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 My World, Open the Louisiana Project File, and Add a New Layer


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Classify Point Features by Field

10 edit appearance The Edit Appearance window in My World.

Open the Edit Appearance window for the Louisiana Cities layer by double-clicking the Louisiana Cities label in the Layer List.

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

  • To open the Edit Appearance window for the Louisiana Cities layer, double-click the Louisiana Cities label in the Layer List.
  • Drag the Edit Appearance window to a location where you can see both it and the map at the same time.
    1 esit appearnace and map

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Classify Point features by Equal Interval

In the Edit Appearance window for the Louisiana Cities layer, graduate the size of the symbols to emphasize the Population of Louisiana cities in the year 1990. Select the following options:

Double click on the layer name to open the Edit Appearance window.
  • Choose Shape by: Uniform and Circle

  • Choose Size by: POP90
  • Size Range Medium
  • Size Count 5
  • Classify by Equal Interval

  • 3 edit app and map EI
  • Choose Color by: POP90
  • Colorscheme Black-Red
  • Color Count 5
  • Classify by Equal Interval
  • Click Apply and click Close

edit appearnce and mpa EI 2
This is the completed map. The resulting map consists of mostly black dots. In fact, 386 of the 391 cities are represented by small black dots.
5 map EI

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 Edit Appearance 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 Edit Appearance 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 are not represented in a way that helps reveal patterns on the map. Why, you might wonder? Use analyze mode to carry out a query in order 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 is greater than or equal to 219531).
The result is two cities: Baton Rouge and New Orleans. They are colored yellow on the map.

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?

Try a third method of breaking up the data called Natural Breaks.

To set Natural Breaks breaks:

This is what the map looks like after symbolization using Natural Breaks.
10 map NB

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

Equal Interval Map
5 map EI
Quantile Map
7 map quantiles
Natural Breaks Map
10 map NB

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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 Edit Appearance window, double 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 Colorscheme pull down menu and choose a different palette of colors, such as Dry Rainbow or Red-White-Blue. 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 Louisiana 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

  • Turn on U.S. Rivers and the 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 (from anther source) shows the early settlements in the 1700's.
      Historic posts and settlements 1700\
    • What other questions might you ask of this data?
    • How did people move inland and what crops did they grow?
  • Click on the Historic Settlements map with the pointer tool and note the arrow that moves around on the legend as you do so.

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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 My World

    Movie Icon Classifying polygon features in My World

    Movie Icon Classifying the historicsettlement layer in My World

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    iPod Versions

    Download these version to play on your iPod or iPhone.

    Movie Icon Classifying polygon features in My World

    Movie Icon Classifying polygon features in My World

    Movie Icon Classifying the historic settlement layer in My World

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