A map displays one or more data sources, which describe
the map components. A data source provides the map components, such
as polygons and lines, and their properties. If you import more than
one data source, each is placed into a separate layer that forms part
of the map background.
Layers are also used to contain other information, such
as grids, labels, terrain analysis and measurements. You can control
how much information is displayed at any one time by selecting which
layers to make visible. See
Map themes and zoom levels for more
information.
Most layers allow users to define styling parameters,
such as
color,
border thickness, or
labels for the graphical components.
You can adjust the order of layers and the transparency of its content
so that one layer does not obscure the information in another (see
Managing map layers).
A component is the lowest level of object and can be
considered as a polyline with properties such as name
and position
(used
for streets for example), or as an area with properties such as name
and color
(used
for countries for example). Component properties can be used for labeling
or filtering and are displayed in the tooltips (if activated on the
map), and in the Property pane of the selected layer.
The purpose of layers is to provide a hierarchical organization/decomposition
of the map represented using a given style. There is no limit to the
number of layers you can define. The contribution that each layer
makes to the overall theme is known as a layer style.
For example, a map background layer could consist of
ground transportation with roads, motorways, streets, and tunnels
defined as sublayers. Or the map background layer could be based on
legal boundaries with countries, states, counties, cities, and blocks
defined as sublayers.
The following figure shows an example of a map showing
road, highway, and motorway layers.
Layers are displayed in a pane in the Map Builder under the Map Layers tab.