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Chapter 9
Working with Map Layers
About Map Layers
Layers are like separate transparent sheets on which your map data is drawn.
Every map generally contains a minimum of one layer, but because layers are
so useful for organizing and working with your data, a map typically will
contain several layers. At minimum, you must have a separate layer for each
type of data you use in the map. You cannot display points and polygons on
the same layer, for example.
You can create a layer and use it for a specific map, or save it as a separate
map layer file (MLF) and use it in several different maps. A map can contain
multiple layers of the same type, such as multiple polygon layers, each of
which you can set up independently of the others. You can also create collec-
tions of related layers, called
layer groups
to help you organize layers in a map.
You can create dynamic and static map layers. A dynamic layer stores only
the layer styles (such as color, style, and symbology) in the map (MWF) file,
not the map data, thus minimizing file size. When you access a dynamic map
layer using Autodesk MapGuide Author or Autodesk MapGuide Viewer,
Autodesk MapGuide Server sends the map data for the layer on demand. As
you zoom in and out on the map, the Server sends the data for the visible
area only, not for the entire map. Dynamic layers are most appropriate for
medium to large data sets and for maps that cover a large area.
A static map layer stores a snapshot copy of the layer data for the entire map
window and embeds it in the map file. Because all of the data is already in
the map, the layer takes a little longer to load, but zooming in and out is
faster than with dynamic layers, because no additional data needs to be
downloaded from the Server. Note that if you change the map’s default
center and size or map projection, Autodesk MapGuide Server does need to
rebuild all static map layers, as it does with dynamic layers. Static map layers
are most appropriate when the data set does not change often, the size of the
data set is relatively small, and the map covers a small area. Also, because the
data is contained within the map itself, static layers are best used when data
security is not an issue.
Autodesk MapGuide Author draws layers in order of increasing priority
starting with priority 0, then priority 1 on top of layer priority 0, and so on,
until it draws the layer with priority 100 last, on top of all other layers. The
drawing order is reflected in the Viewer legend and in the Map Explorer,
where the layer with the lowest priority is at the bottom of the list, and the
layer with the highest priority is at the top of the list. For information about
changing a layer’s priority, see “Specifying General Properties for Layers” on
page 153.
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