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Selecting Layers
The GIS Layers pane has check boxes that allow the user to turn on and
off geographical layers in the map view. Check any of the layers then
press the 'Update Map' button to update the current map view with the selected
layers. Some layers have labels available. See the
Map Labels section below for more about labels. Some
layers also have the option to choose an Active layer. See the
Active Layers section below for more about the use of active
layers to select monitoring sites and display detailed metadata.
When the Metadata browser is first loaded by your
browser the RPO layer is displayed by default. The RPO layer
shows states color coded by their representative RPO. Note that
un-checking any layer that displays a typical map view (such as RPO or Cont.
U.S.) will render a map view without a base map.
The layers are ordered from
top to bottom in the GIS layers pane so that upper most layers are displayed on
top of lower layers. For example, if both RPO and N. America
layers are checked, the RPO layer will be visible on top of
the N. America layer. For the three layers that
display the continental U.S. precedence has been built in to the browser so
that only the upper most selected layer of these three layers can be selected
at one time. This feature is built into avoid superimposition of multiple
layers with the same extent.
Layers
Roads show major interstates in the Continental U.S.
Rivers show major rivers in the Continental
U.S.
Cities
show point locations of cities in the Continental U.S. with populations over
25,000. The size of the city icon is related to the city population.
Urban Areas shows major U.S. urban areas.
US Parks
show NPS park lands in the U.S. The parks are divided into Class I and Class II
Areas.
Class I Areas shows
Class I Areas in the U.S.
Counties
show U.S. county regions including counties in Alaska and Hawaii. Note,
the Counties layer takes precedence over the RPO and Cont. US
layers. That is, the RPO and Cont. US layers layers will be
automatically de-selected if the Counties layer is selected. This feature
is built into the metadata browser to avoid superimposition of multiple layers
with the same extent.
Cont. U.S.
shows states in the Continental U.S. This is a high-resolution
layer. The Cont. US layer takes precedence over the RPO layer.
RPO shows states regions in the Continental
U.S. The states are color coded by their representative RPO. This is a
low-resolution layer.
Alaska, Hawaii, Caribbean layers are
high-resolution layers of the respective states or regions.
Canada, Mexico, and N. America layers are
low-resolution layers of the respective states or regions.
Note, some some layers are available as
low-resolution layers and some as high-resolution layers. Low-resolution
layers have less geographical detail and are sufficient for large scale
views. If you want to zoom in and see more geographical detail, choose a
high-resolution layer. For example, the RPO layer has sufficient
resolution to display a large scale view of the U.S., however if one zooms in
on a specific area, such as the San Francisco Bay Area, the Cont. U.S. layer
will provide more geographical detail. The advantage of low-resolution
layers is they will allow the Metadata browser application to run faster.
Also, keeping the selected layers to the minimum necessary to provide desired
information will help the Metadata Browser run faster.
Active Layers
If an active layer is selected from the GIS layers pane areas defined
in the active layer can be selected from the map using a mouse click.
Active layers that define regions are associated with monitoring sites and can
be used to select monitoring sites by region. Active layers that define points
or lines (such as the Cities and Rivers layers) can be selected but only
information about the layer will be returned.
All the program layers that display monitoring sites
are active layers. Clicking on any site icon will display metadata about
the selected site.
Some layers are active by default and some are
optionally available as active layers. If an optionally available active
layer is selected and the map is updated using the 'Update Map' buton the layer
becomes active and the layer name will appear in red italics. For
example, when the Counties layer is made active it will be displayed as
Counties in the GIS layers pane. If the Counties layer
is active, clicking within the boundaries of any county will display metadata
about the selected county along with metadata for monitoring sites within that
county from all currently selected programs.
Optionally active layers facilitate selection when
overlapping layers are displayed. For example, if monitoring site are
displayed over the RPO layer, selecting individual sites is much easier if the
RPO layer is not active.
To remove a layer from the map view both the active
layer and non-active layer checkboxes must be deselected. |
