Pima County Geographic Information Systems

Overlapping Layers in MapGuide

This page explains overlapping layers that are on top of each other in MapGuide maps. Also see Overlapping Data in a MapGuide Layer for overlapping map features within one map layer.

Layers displayed on MapGuide overlap each other. Looking at the map, we really see (and sometimes see through) a "stack" of layers. You can think of each layer as if it was printed on a sheet of clear plastic or cellophane. The layers in the stack are in the same order as the list of layers in the legend to the left of the map. The layers at the top of the legend on the top of the map stack. We use point/line/polygon/imagery grouping so one layer doesn't unnecessarily cover another layer. Here's what makes up the stack of map layers:

• Points and lines: We put layers that display as points or lines toward the top of the legend. Streets are an example of layers that are lines. We can see around these points or lines to layers below them in the stack that where the map features have area.

• Polygons: Parcels, subdivisions, and zoning are examples of layers that show areas and are next in the stack. Areas are shown as polygons three different ways (and in this order):
  1. Some polygon layers are shown with complete transparency. Parcels are the best example. We can see the parcel outlines and can see right through the parcel areas to any layers that might be under them.

  2. Next in the stack are layers that are translucent. That is, the areas have color or hatching, but we can partially see through them to layers lower in the stack. Subdivisions are an example of a layer displayed with translucent polygons.

  3. The lowest of the polygon layers are those displayed as solid polygons. They are filled with a solid color that we can't see through. There may be map data underneath a solid color polygon, but we can't see it. Over time, we are changing most solid polygon layers to be translucent so we can see through them.

• Imagery: Orthophotos and other imagery are a the bottom of the stack and legend. These layers are all opaque and we can't see through them. If two different orthophoto layers are turned on at the same time, then we only see the orthophoto on top.

Layer order affects more than just what the map looks like in two important ways.

1. Map tips: The yellow "map tip" we see when hovering over a map feature always shows information only for the top layer. We may be able to see through transparent or translucent areas to layers lower in the stack. However, the map tip always shows information only for the layer on the top of the stack. This is true even for completely transparent polygons. The best and most prevalent example of completely transparent polygons is the Parcels layer. Even though we can often clearly see other layers under parcels, the map tip inside a parcel's area always shows the parcel's data and not that of a layer underneath the parcel in the stack. If you want to see the yellow map tip that identifies a map feature displayed underneath parcels (or any other transparent or translucent layer) you need to turn of the transparent or translucent layer first.

2. Double-clicking: You can double-click on a map feature to get more information about the map feature. The map feature may be a point, line or a polygon. For instance, you can double-click on a parcel and see a page of information about that parcel. Keep in mind that not all map layers allow double-clicking to see more information. If you see the pointing-hand cursor, then you can double-click for more information. Just like the map tip is only for the layer on top, double-clicking always shows information for the layer on the top of the stack. You may see a map feature under a transparent parcel or a another layer's translucent map feature, but the double-click is always for the top layer. To double-click on a layer that's lower in the stack, turn off the layer or layers above it first.