Using Spatial Data with SAS/GIS Software

Changing the Default Characteristics of a Map

Once you have imported a new map or loaded a new SAS/GIS software spatial database from a commercial vendor, you may want to change some of the default characteristics of the map to suit your needs and preferences. Some of the following characteristics you can change to include the following:

Projection system used to display the map
Scale mode and units
Background color for the map area
Layers that are initially displayed or hidden
Level of detail for map features.

To learn about other ways in which you can customize the appearance of the map, see Chapter 5, "Customizing Maps," in SAS/GIS Software: Usage and Reference, Version 6.

Selecting a Map Projection

Projection is required to represent spherical features like the earth's surface on a flat medium like a display screen or printed page. SAS/GIS software supports a wide variety of projection methods, but it assumes by default that the coordinate values in the newly imported spatial data are arbitrary Cartesian (X/Y) values (except for TIGER and DYNAMAP, which assume latitude and longitude degrees). However, the coordinates in the MAPS.COUNTY map data set are actually latitude and longitude values in radians. As a result, the initial Carolinas map in Initial Display of Imported SAS/GRAPH Map is elongated and reversed right-to-left.

To change the projection system that is used for the spatial data, you use the GIS: Projection Options window. Open the GIS: Projection Options window with the following selections from the GIS Map window's menu bar:

Tools Map Properties Projections...

In the GIS: Projection Options window, Storage Projection System specifies the system that is used to interpret the stored spatial data, and Display Projection System specifies the system that is used to project the interpreted spatial data for display in the GIS Map window. Use the down-arrow controls to select Lat/Lon for both Storage Projection System and Display Projection System. Also in the storage system parameters, select W for Hemisphere and 1 for the Units Multiplier. Then select [Close] to close the GIS: Projection Options window and apply the new projection specifications.

Note: This example uses the same projection system for the Storage Projection System and the Display Projection System. [cautionend]

The spatial data are reloaded into the GIS Map window by using the new projection systems, the projected version of the map is displayed as shown in Changing the Initial Map Projection.

Changing the Initial Map Projection

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Selecting the Units System

By default, the scale feedback for the newly imported map uses metric units. Use the GIS Map Options window to set the units system of a new map. Open the GIS Map Options window with the following selections from the GIS Map window's menu bar:

Tools Map Properties Map Options

Select English for the units system to change the scale mode to mi/in (miles per inch), and then select [Close] to close the GIS Map Options window and apply the change to the map feedback area as shown in Changing the Initial Unit System.

Changing the Initial Unit System

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Selecting a Background Color

By default, the map area is assigned a white background. Use the GIS Map Styles and Colors window to choose a different background color for the map. Open the GIS Map Styles and Colors window with the following selections from the GIS Map window's menu bar:

Tools Map Properties Colors...

Use the pull-down control for Background to display a list of the standard SAS colors and select Blue, and then select [Close] to close the window and apply the new color choices as shown in Changing the Initial Map Background Color.

Changing the Initial Map Background Color

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Choosing Which Layers Are Displayed

By default, only the first layer in the layer bar is displayed; other layers are hidden. To select which layers are displayed or hidden, click the mouse selection button on the corresponding layer bar buttons. Selecting a layer that is currently shown hides that layer, while selecting a layer that is currently hidden displays that layer.

In the example map, use the mouse selection button to hide the COUNTY layer and display the STATE layer as shown in Changing the Initial Active Layers. When you are finished viewing the STATE layer, turn the COUNTY layer back on.

Changing the Initial Active Layers

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Changing the Level of Detail

In the spatial database, SAS/GIS software distinguishes between the coordinate points that are necessary to represent features minimally and those that provide extra detail. For example, the starting and ending intersections of a segment of a street are considered fundamental points, while additional points that represent the curves between the intersections are considered extra detail. By default, SAS/GIS software uses detail points for all layers if they are available. To turn off detail points for all features in the map, make the following selections from the GIS Map window menu bar:

View Detail

The checkbox or check that appears next to the menu item when detail points are used disappears when detail is turned off.

With detail turned off, map features are drawn more coarsely but more quickly, since fewer lines are drawn. Changing the Initial Detail Level shows the resulting map. Turn detail back on to provide full detail to the map.

Changing the Initial Detail Level

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