So-called Dynamic Internet Map Servers that allow data download
operate as either stand-alone services that use a browser window
(see for example the outstanding example at
http://seamless.usgs.gov/)
or with an interface that allows viewing in ArcCatalog and ArcMap.
Though only a handful of the latter presently (12/2002) exist,
they are increasing in number. They can be outstanding data
resources, but it is far from obvious how to download data from
them. Follow the steps below to do so.
1) Add an internet map server to ArcCatalog following the
directions in the Help file, or simply use the one already
available (www.geographynetwork.com)
near the bottom of the ArcCatalog file tree, shown at the red
arrow below.
Note
from the figure two other servers that you can connect to; the
TNRIS server is outstanding for Texas data.
2) Open a new project in ArcMap and add the server as a
layer, as you would with any other data. If it’s a server
network (e.g. the geography network) then you will have several
servers to choose from. For example, the same seamless NED data
available at the link given above can also be loaded as a layer
from within the geography network server.
3) If you’re lucky and there’s plenty of bandwidth available
(i.e. it’s early morning or late night), the layer will soon
load with a legend containing numerous entries. The legend
should behave similar to any other map; you can turn sublayers
on and off, some will be visible only at larger scales, etc.
4) Use standard selection techniques to isolate the data you
wish to download. Some sublayers will not be selectable, others
may have very limited options for selection.
5) Once you’ve made your selection, Right-click on the title
of the layer in the Table of Contents that contain the data and
select Data>Export Data.
6) Choose to export as shapefile or geodatabase feature
class, name your file and save to a location on your local or
network (y:) drive.
I have used this technique to download vector hypsography (topo.contours)
from the TNRIS for several locations in Texas. As far as I’m
aware, at the time of this writing (4/03) this is the only way
such data can be gathered. Don’t attempt it between 11 AM and 9 PM
– even with an100 base T connection like ours in the Department,
there is not enough bandwidth to access large IMS layers within
ArcMap without being totally frustrated.
Note on 11/25/03 - Discussion of new software to access
internet map servers and background information on Web Map
Services and software was a recent topic in the
GIS Monitor.
