Internet
Map Server - a Quick Start Primer
The ARC
Internet Map Server (ArcIMS) is a program for displaying and querying
maps over the Internet. The maps are interactive - a user can zoom in
and out of maps, with different amounts of detail being presented at
different spatial scales. IMS allows different kinds of map layers (roads,
land use, water bodies) to be turned on or off, so customized maps may
be created. A user can also perform interactive queries to collect information
about different items on the map. It is thus a fairly powerful way to
distribute GIS data over the Internet.
The following
primer covers the basics of using IMS - how to get and retrieve information.
In the few minutes it takes to read this, you'll learn all you need
to know to complete the map-based curriculum exercises in Water on the
Web.
Getting
to the IMS
Most of
the curriculum exercises that use IMS have links to a particular lake
or watershed used in that lesson plan. Clicking on the link causes a
lot of things to happen - it wakes up a copy of ARCVIEW residing on
the WOW server, loads all the appropriate data, and delivers the data
over the Internet to the web browser on your computer. As a result,
this link is slower that most web links, although in most cases the
maps are delivered in under a minute. Remember, in the old days, we
had to wait for monks to draw out these maps, and they took a really
long time, so be patient!
The IMS
Display
The following
figure shows the IMS display for the Medicine Lake watershed. The screen
has four primary sections:
Useful
things to know:
Map layers
composed of lines, such as roads and streams, overlay quite easily.
Layers which are based on polygons that cover the map, such as land
use or soil types, however, can only be viewed one at a time. For this
reason, a map layer may be 'hidden', i.e. the layer might be turned
on, but you won't be able to see it. By convention, IMS draws layers
at the bottom of the legend first. In the figure above, the Land Use
map is drawn first, followed by the Parks layer, followed by Game Refuges,
etc. If a layer seems hidden, turn off the layers above it to make it
visible.
Most of
the tasks you will perform in IMS involve setting up a view of the map
that shows what you want to see, and using the Identify or query tools
to retrieve information on map objects. The Identify tool returns information
in a data table that opens either in a new browser window, or within
the current map window. You can also measure distance, construct sophisticated
queries on tables, or select and analyze multiple features. The best
way to learn what these tools do is to try them!
Information
from the data display windows can be copied and pasted into a WOW exercise
data table using standard Windows/Mac copy and paste conventions.
Note that
IMS stores information with a lot more precision than you really need
(or is justifiable, given the inherent error in the mapping process).
For example, the Identify tool reports the area of one of the Farmsteads
as 27711.57356 square meters. Feel free to round this to 27712 square
meters. Heck, 2.8 hectares would be OK. (10,000 m2/ha).
More Help
Further
information on using IMS can be found at the ESRI web site under http://www.esri.com/software/arcview/mapcafe/index.html
is used. Use
the Refresh Map button will redraw the screen to update changes
in the Layers window. The Toggle Tool in the upper left corner
of the toolbar will toggle between this Layers window and a Legend window,
which provides a color and symbol legend for each of the map elements.