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gis quick start primer

IMS Display

Query function
  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:

  • The Toolbar for performs various map operations. You can hover over the Toolbar elements in the figure below to obtain a description of their functions - this feature works in the actual IMS session as well.

    The toolbar at the top of the display contains a number of icons that allow you to manipulate the map. Their functions are described below:
  • Toggle between legend and layer list (newer versions show both without toggling)

    Toggle overview map - allows you to view the overview map

    Zoom In - allows you to obtain a close-up view of an area of the map. A key feature of the zoom tool in IMS is that it can be programmed to show progressively more information as you zoom in.

    Zoom Out - very similar to Zoom In, but the other way

    World - Zooms out to the furthest extent of the map

    Zoom to active layer - maximizes the active layer in the view window

    Back to last extent - fancy way of saying go back to last view

    Pan - allows you to move the map back and forth, up and down. This is useful if you have zoomed in to the map and want to see something that is off the screen.

    arrows Arrows - allow you to mone the map to the North, South, East or West. This is useful if you have zoomed in to the map and want to see something that is off the screen.

    Hyperlink - allows you to link to data. Links can also be accessed via the Identify tool.

    Identify - An important tool, it allows you to retrieve information about a particular map object  

    Query - Ask questions within or across map layers. Click here for a tutorial on the query function.

    Find - allows you to search the active layer

    Measure - allows you to measure the distance between 2 points. Keeps a cumalative tally of measurements until cleared with the Clear selection button.

    Set Units - sets the units for the measurement tool

    Buffer - allows you to created a visual buffer of a set size around a selected feature.

    Select by Rectangle - used to select a feature in the active layer

    Select by Line/Polygon - used to select a line or polygon in the active layer

    Clear Selection - zeros the measurement tool

    print Print - sends the map to your local printer  

  • The Layers window on the right presents an interactive legend that allows different map elements to be viewed and queried. The Visible checkbox determines which layers are displayed. The Active radio button determines which layer returns information when the Identify Tool 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.
  • The central map viewing frame diplays the visible layers. This map can be manipulated (zoom, pan, query) using the Toolbar tools.
  • The information window below the map returns results from map queries.

Toggle Overview Toggle Overview

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.

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date last updated: Tuesday May 18 2004