How do these interactive internet maps work?

Your web browser, usually NetScape or Internet Explorer, is displaying this web page to you by translating a document that the Map Center site sent to your computer over the internet. The document is a collection of text and pictures plus instructions for how to display them in your browser's window. Together, the text, pictures, and instructions are called HyperText Markup Language (HTML).

When you click the mouse on images or buttons and select from lists of choices, like asking to see a map of a school or landmark, you are sending a long line of text back to the Map Center site. In this long line of text is a record of the page you were looking at when you made your request--if you were looking at a map already and decided to zoom in closer, the long line of text will include the extents of your map before the zooming happens and the command to zoom in.

The Map Center site is a group of networked computers called a "server" that listens for requests from the internet. When you send your long line of text asking for a map, the server passes your request to a special program that is always running called the Internet Map Server (IMS). This program is written in the Microsoft Visual Basic programming language and Environmental Systems Research Institute's (ESRI) MapObjects components. The IMS breaks up the long line of text into separate parts and uses each part as instructions for drawing a new map. It takes a snapshot of the new map and turns the snapshot into a GIF or JPEG image that your browser can display. Then the IMS sends the image back to your computer as part of a new HTML document. If you just zoomed in, the new HTML document would be the same as the old one except for the map image.

Web sites that let the public decide what sort of map they want to see (by zooming or panning or changing the map scale, for instance) are called "interactive" sites because the public gets to interact or send information back and forth between their computers and the server. Some Internet Map Servers, like OUSD's, use images to display the maps. The other strategy for displaying maps is to send special data objects that your browser knows how to draw and interpret if you also load a special "plug-in" into the browser. For simplicity's sake, OUSD uses the image strategy rather than the plug-in strategy in hopes of opening the site to all visitors, no matter how technically skilled they may be.

The software that runs the Map Center site is a combination of products from different companies. The server is Microsoft's Internet Information Server. The Internet Map Server is Environmental Systems Research Institute's MapObjects Internet Map Server in conjunction with Microsoft's Visual Basic. The computer supporting these products is a Windows NT Workstation with a 450 Mhz processor.

Map Center was produced by Gary Meisner (OUSD), directed by Gil Brenum (OUSD), and built by Jonathan Lowe (Local Knowledge Consulting) for use by the public school students and community members of Oakland, California.

Frequently Asked Questions:

1. Where did the map data come from?
2. How do these interactive internet maps work?
3. Why doesn't Map Center mark the right house on the Air Photo when it finds my address?
4. How many maps have these sites created?
5. Why do Map Center maps have a different look and feel from other internet maps?

    GIS Website design by Local Knowledge Consulting

Copyright Oakland Unified School District. All rights reserved.
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