While it is conceivable that one could effectively employ XMap without ever clicking the Draw tab, the Route tab, or even the GIS tab, it is implausible that anyone could operate the software in a productive manner without addressing Map Data. In short, Map Data is the essential tab. At a superficial level, it is a fairly straightforward component of XMap, its primary function being to allow a map view to be saved for later retrieval. That said, there are a number of less obvious features that can allow you to do some very interesting things within the Map Data tab.
Dual Map Display
Perhaps the dual map display is one of the more obvious features of the Map Data tab, but it is a very powerful function nonetheless. The two separate windows in the tab area provide an opportunity for the contents of both the primary and secondary maps to be customized. For instance, you can display imagery on one side and the topographic map data in the adjacent window by simply selecting or clearing the appropriate check boxes next to each dataset. The dual map windows can also be used to render maps at different zoom levels, simultaneously providing a local map and a regional perspective.
Customizing the Contour Interval
The contour interval, as represented on the Control Panel to the right of the map window in XMap, is the difference in elevation between adjacent contour lines on the map. Contours are generated dynamically and the interval decreases as the map display is zoomed. For example, at data zoom level 11, the contour interval is 100 feet while at level 14, it is 20 feet. This ensures that the concentration of contours is appropriate for each display level or scale. There are occasions when the contour interval at certain zoom levels might need to be adjusted. For instance, in a mountainous area, the contour interval may need to be increased to unclutter the map, while in a lowland area you might choose to space the contours closer together to emphasize the terrain.
The contour interval can be adjusted using the following procedure:
- In the Primary Map window in the Map Data tab, click the plus sign next to Reference Data and then click the plus sign next to Topography.
- Right-click Contours and select Properties
- The resulting dialog box offers a drop-down list from which Default, High Density, Low Density, or Custom can be selected. High Density decreases the contour interval across all zoom levels; Low Density increases the interval; while custom allows the precise spacing at each zoom level to be manually configured.
- If Custom is selected, the next window in the sequence provides the opportunity to determine the contour units in feet or meters, the number of major (labeled) contours per minor, and the overall contour spacing for each selected zoom level range.
- After clicking Next again, you can adjust the overall zoom level range within which contours will appear on the map by sliding the arrows back and forth.
- Finally, you can select the map windows in which contours will be displayed before clicking the Finish button.
Note that a custom contour configuration is saved as a component of the current XMap project, which ensures that you will not need to repeat this process each time you use XMap. In fact, if you need to continually adjust the contour interval, it is a good idea to establish several contour configurations and save each as its own project file.
Adjusting the Shaded Relief Pattern
XMap’s topographic shaded relief provides a shadow effect derived from the underlying digital elevation model that visually enhances the terrain on the map. By default, this shadow effect is based on a hypothetical light source emitting from the northwest at an inclination of 40° above the horizon.
In the Map Data tab, Shaded Relief is listed under the Topography section of the Reference Data, just below Contours, which was described above. Accessing the properties of the shaded relief pattern using the same right-click process as before offers the ability to adjust the bearing of the light source, the inclination value, and the brightness of the shadow effect. For example, you could display a map showing the terrain at sunrise by changing the bearing value to E (for east).
Raster Layering
A raster map is one that is represented by an array of different colored pixels, the same as in a conventional digital photograph. A vector map is made up of geometrical points, lines, and polygons which are used to represent geographic objects stored in a database. The XMap North America Topographic Data is an example of a vector map dataset.
When displayed in XMap, raster map layers, such as aerial imagery or scanned USGS quad maps, will appear on top of the corresponding vector map, which usually obliterates the view of the vector features. The Map Data tab in XMap offers a way to adjust this layering hierarchy so features such as roads or contours can be rendered on top of a raster layer.
Follow these steps to adjust the layering properties of a raster layer:
- In the Map Data tab, click the plus sign next to the appropriate data type (for example, Color Aerial Imagery) and then click the plus sign next to specific file name. This will reveal the format of the raster layer (such as Color DOQQ).
- Right-click this data format name and select Properties. Usually the first dialog box offers the option to select a transparent color. It is usually not necessary to adjust this setting.
The next dialog box is used to adjust the layering of the selected raster layer relative to the underlying vector dataset. From the Raster Data Position drop-down list, select the component of the vector data that you want to display on top of the raster layer (such as roads). Note that whatever feature is selected, each of the items above it in the list will also be pushed to the top of the layering hierarchy. Make sure to click the Add/Change button before proceeding.- It is possible to establish a different layering sequence for selected zoom level ranges. For example, the Raster Data Position setting could be configured in such a way as to display just the aerial imagery until data zoom level 15 and overlay the roads from levels 16 to 20.
- Click the Next button to set the data zoom level range within which the selected raster layer will appear and click Next again to determine which map windows will display this data.
- Finally, if your current project contains more than one instance of the selected data type, you will be prompted to configure each of these raster datasets with the same parameters in the selected layer.
This raster layering process is often used in conjunction with the Map Features function in the Options area of XMap to simultaneously filter the display of vector features and overlay this modified data on an aerial image.
Displaying a Coordinate Grid
Reading this article, you will have noticed that most of the configuration options in the Map Data tab are accessed by opening the properties dialog box for each component. The coordinate grid function continues this trend. By default, grids are not displayed in XMap; however, they can be turned on from within the Map Features tab in the Options window or using the check box next to Grid Lines in the Map Data tab. The grid lines feature is accessed by clicking the plus sign next to Reference Data and then clicking the plus sign next to Grids and Zones.
By right-clicking Grid Lines and selecting Properties, you can adjust the data zoom level range within which the coordinate grid will appear as well as the map window within which the grid will be displayed. Latitude and Longitude is the default format; however, UTM, State Plane, the Military Grid, or the U.S. National Grid can be selected from the Display tab in the Options area of XMap.
All of the datasets listed in the Map Data tab can be customized in certain ways. By selecting the properties option while right-clicking a particular layer or feature, you can often create a thoroughly unique map that accentuates the display of whatever data layers you have imported or created in XMap.
