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

• Launch My World by double-clicking its icon on your desktop or by clicking its icon in the Dock (Mac) or Launch Bar (Win).
• Choose File > Open Project ..., navigate to Applications/My World/data/LouisianaMW, select the LA_Rivers.m3vz file, and click Open.
  
• A map of Louisiana is displayed when the project opens. Parishes are shown in tan and the Mississippi River is blue.
• In Visualize mode, select File > Import Layer from File , navigate to the LouisianaMW folder, select cities.shp, and click OK. Cities should now be the top layer on your map. Note: The cites layer is automatically turned on when it is added.
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Classify Point Features by Field

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.

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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:

• Choose Shape by: Uniform and Circle


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


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

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:

• Choose Shape by: Uniform and Circle


• Choose Size by: POP90
• Size Range Medium
• Size Count 5
• Classify by Quantiles


• Choose Color by: POP90
• Colorscheme Black-Red
• Color Count 5
• Classify by Quantiles
• Click Apply and click Close

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

• Return to Edit Appearance window.
• Under Classified by, switch between Equal Interval and Quantiles. In each case, examine the Legend and the number of records in the Map window.
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These are the two Legends windows. Look at the Range of the data and the number of records in each group.
Equal Interval Legend

Quantiles Legend

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.

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:

• The Edit Appearance window for the cities layer should be open. If not, double-click the Louisiana Cities layer in the Layer List.
• Click the Size tab.
• Set Choose Size by: to POP90 and the Size Range to Medium. The size count should be 5.
• In the Classified by drop down menu, choose Classify by: Natural Breaks to reset the class breaks.
• Adjust the Color to Natural Breaks as well.
• Click Apply and click Close
• Close the Edit Appearance window.

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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.

• Turn on and activate the Parishes layer.
• Choose Fill Color for the Parishes by NAME.
• Choose Field NAME, Colorscheme: Random, Transparency: O%.
• Click Apply.
• Before clicking Close, explore other Color Schemes and other Shapes of fill for each Parish.
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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.

• Change the Parishes fill to transparent. In the Fill Color menu, adjust the Transparency slider to 100%.
• This choice leaves only the outline on the polygons.
  This technique is very handy when you want to be able to see through a reference layer to a layer below.
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To change the Parishes fill to transparent, move the slider to Transparency 100% in the Fill Color window.

The Parishes layer is now transparent.

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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.

• Activate the Parishes layer and open the Edit Appearance window.
• Select the following options:
• Choose Fill Color by Pop90_SQMI (population per square mile in the year 1990).
• Colorscheme Blue Ramp 2.
• Choose Classify by Quantiles.
• Click Apply and click Close.

The Parishes are now color coded by Population Density.

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.

• Turn off the Louisiana Cities and Parishes layers

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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?"

• Add a new layer to show the historic settlements in Louisiana. Click the Import New Layer From File button. Navigate to the Louisiana folder. Click once on historicsettlement.shp file to select it. Then click Open.
• historicsettlement should now be the top layer on your map. Notice that the layer is automatically turned on when it is added.
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1. Click the Import New Layer From File button. Navigate to the Louisiana folder. Click once on historicsettlement.shp to select it. Then click Open.
2. Move the new layer down in the Layer list. Put it below the point and line layers, and just above the Parishes layer. Notice that when it is added it is all one color, not very informative!