Preparing Spatial Data

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 might want to change some of the default characteristics of the map. Some of the characteristics you can change 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

A 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 newly imported spatial data are arbitrary Cartesian (X/Y) values (except for TIGER and DYNAMAP files, for which SAS/GIS software assumes 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 in the GIS Map window. Use the drop-down arrows 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. 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. It is not required that the two use the same projection system unless the Storage Projection System is arbitrary Cartesian data. [cautionend]

The spatial data is reloaded into the GIS Map window by using the new projection systems, and the projected version of the map is displayed as shown in the following display.

Changing the Initial Projection

[Changing the Initial Projection]

Selecting the Units System

By default, the scale feedback for a newly imported map uses metric units. You 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). Select Close to close the GIS Map Options window and apply the change to the map feedback area as shown in the following display.

Changing the Initial Unit System

[Changing the Initial Unit System]

Selecting a Background Color

By default, a map area is assigned a white background. You use the GIS Map Styles and Colors window to choose a different background color for a 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 drop-down arrow for Background to display a list of the standard SAS colors and select Blue . Select Close to close the window and apply the new color choice as shown in the following display.

Changing the Initial Background Color

[Changing the Initial Background Color]

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 corresponding layer bar check boxes. Deselecting a layer that is currently shown hides that layer, while selecting a layer that is currently hidden displays that layer.

In the example map, select the appropriate check boxes to hide the COUNTY layer and display the STATE layer as shown in the following display. When you are finished viewing the STATE layer, turn the COUNTY layer back on.

Changing the Initial Active Layers

[Changing the Initial Active Layers]

Changing the Level of Detail

In spatial databases, 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 the detail points for all features in the map, make the following selections from the GIS Map window menu bar:View Detail

With the detail turned off, map features are drawn more coarsely but more quickly because fewer lines are drawn. The following display shows the resulting map. Turn the detail back on to provide full detail to the map.

Changing the Initial Detail Level

[Changing the Initial Detail Level]

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