|Using Spatial Data with SAS/GIS Software|
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:
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:
In the GIS: Projection Options
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
System. Also in the storage system parameters, select
Units Multiplier. Then
select [Close] to close the GIS: Projection Options window
and apply the new projection specifications.
example uses the same projection system for the Storage Projection System
and the Display Projection System.
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
|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|
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
|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:
Use the pull-down
Background to display a list of the standard SAS colors and select
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
|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
|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:
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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Copyright 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.