Overlay Maps

It is possible to combine several maps by overlaying the maps. You can overlay any combination of contour, base, post, color relief, vector, or surface maps. Overlays can contain only one wireframe, however. When you overlay maps, the overlays use a single set of X, Y, and Z axes and the maps are positioned according to the Map coordinate system. If two or more maps use the same limits, they will overlay on top of one another. If maps cover adjacent areas, overlaying maps places them in the correct position relative to one another and creates a single set of axes that span the entire range. Overlaid maps become a single object and are moved and scaled as a single entity.

Consider a contour map and a base map that displays the outline of a lake on the contour map. The limits of the base map are the XY extents of the lake and are not the same as the contour map limits. If you create both the base map and the contour map in a single plot window, they do not overlay correctly because by default the maps are scaled differently. In addition, each map uses a different set of XY axes. If you select both maps and then click the Map Tools | Map Tools | Overlay Maps command or the button, the contour map and the base map are rescaled and combined into a single map using a single set of axes. The lake is now correctly positioned on the contour map.

Overlays and Wireframes

When you overlay contour, post, or base maps on a wireframe, the maps are draped over the wireframe. The wireframe is drawn in the usual fashion but the base, vector, or contour maps are "molded" over the top of the wireframe lines. Hidden lines are not removed from maps overlaid on wireframes. For example, contour lines are not hidden when the contour map lies over a wireframe.

Overlays and Surfaces

When you overlay maps on top of surface maps, hidden lines are removed and the maps are "molded" on the surface. Surface maps and images, vector files, and even other surface maps can be overlaid. The Overlays tab in the surface map properties contains options for handling color in these cases.

Overlay Exceptions

The Map Tools | Map Tools | Overlay Maps command overlays all selected maps. Most combinations of map types can be overlaid. The exceptions are combining wireframes and surfaces, overlaying raster maps or point clouds with wireframes, and overlaying multiple wireframes. Raster maps include color relief maps, surfaces, and base maps containing an image.

Overlaying Maps

Map layers from different map objects can be overlaid with the Overlay Maps command or with the Contents window. Click and drag map layers into other map objects to overlay maps with the Contents window. To overlay maps with the Map Tools | Map Tools | Overlay Maps command:

Create the maps in a single plot window by choosing the Home | New Map commands. When maps are first drawn in the plot window, they may or may not overlay directly, and each map is an independent object with its own set of axes.
Select the maps you want to combine. When selecting multiple objects you can:
1. Hold down the SHIFT key and click each map layer to be combined in the plot window.
2. Hold down the CTRL key and click each map to be combined in the Contents window.
3. Click Home | Selection | Select All or press CTRL+A on the keyboard to select all the maps in the plot window.
4. Click Home | Selection | Select All | Block Select to surround the maps to be combined.
Choose Map Tools | Map Tools | Overlay Maps to combine all the selected maps. The maps are combined in the correct position based on their coordinates and limits.

Editing Overlays

To edit individual overlays in a composite map, click on the desired map layer in the Contents window. Make the changes in the Properties window. The map layer is automatically updated with the changes.

Hiding Overlays

After combining maps, it is possible to hide one or more of the overlays. To temporarily hide a map, uncheck the visibility box next to the map layer name in the Contents window. The map is redrawn without the selected overlay. To make the overlay visible again, recheck the visibility box. Note that if a surface is made invisible, the overlays are also made invisible.

Deleting Overlays

To permanently remove an overlay from a map, select the map layer and press the DELETE key on the keyboard.