Introduction to JS-GIS

Table of Contents

• About this document and the JS-GIS project
• What is JS-GIS?
• Licensing and Copyright notice
• Credits

• Main index

About this document and the JS-GIS project

This document describes the JS-GIS (JavaScript _Static_ Geographic Information System) data model and JavaScript API. It is intended for programmers who wish to create user interfaces to the geographic data exported from a GIS system according to the JS-GIS data structure, as well as for programmers who would like to implement a JS-GIS publisher for a particular GIS system.

The up-to-date online version of this document can be found at http://jsgis.sourceforge.net/jsgis/doc. Also, check the website for downloadable versions and examples.

The JS-GIS library has been written during the development of the WebStaticMapper project. WSM was initially conceived as a tool for exporting geographic data from MapInfo(R) maps into data readable by a JavaScript-enabled browser. Later on, I split up WSM into two separate projects: a public domain reader, JS-GIS, and a proprietary commercial software, WebStaticMapper.

JS-GIS open source project is hosted by SourceForge. Every kind of contribution is welcome, from testing the library on various browsers, to sending feedback like bug-reporting, notes, requests or impressions. Please visit the project homepage at http://jsgis.sourceforge.net/ if you are interested.

What is JS-GIS?

JS-GIS is a low-cost, effective way to deploy geographic data for many different possible uses. It can be used to distribute GIS data on CD-ROMs as well as on web sites and intranets. All the users will need to read your maps will be a JavaScript and frame enabled web browser.

With JS-GIS, the user is able to:

• view a map and choose among different map themes;
• move along the map (pan) using cursors or a map locator;
• change map zoom;
• locate an object by its centroid coordinates;
• query maps by clicking on them and see the data associated to the identified objects.

Please have a look at the JS-GIS sample page at http://jsgis.sourceforge.net/demo to see how a JS-GIS data browser looks like.

Basically, JS-GIS consists of:

• A data model specifying how to export data from a GIS in a format readable by a web browser;
• a JavaScript API for writing a user-interface to the exported GIS data.

GIS data is exported (published) into the following formats:

• maps are "cut" in tiles and exported as images (i.e. GIF, PNG or JPG images);
• map objects are cut in tiles and exported as HTML imagemap definitions;
• data associated with objects is published in HTML pages referred by the links in the imagemaps.

The geographic area of interest is subdivided into tiles as if it were a chessboard; this subdivision is done for each of the zoom levels defined by the publisher. The export files are generated according to nomenclature and disk location rules: tiles are located according to the zoom level and the map theme and named after row and column position in the "chessboard", while HTML data files are referred by means of the map objects IDs (primary keys), so they usually need to be named following the objects IDs.

The JS-GIS API allows to build a user interface to the published data, by means of:

• classes for handling the publishing project data;
• classes for drawing maps and controls on the web page;
• event handlers for responding to user interaction and defining interface behaviour.

The JS-GIS engine allows for some dynamic operations, such as geographic indexing, point location, dynamic vector object loading (limited to points).

JS-GIS allows to build quickly a simple query interface to geographic data; but being an API, allows for great flexibility and control, too.

Licensing and Copyright notice

JS-GIS is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation at http://www.gnu.org/licenses/gpl.html.

JS-GIS is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

JS-GIS API, JS-GIS documentation © 2001, 2002 by Luca S. Percich
WebStaticMapper © 2000, 2001, 2002 by Luca S. Percich

Author: Luca S. Percich (mailto:luca.percich@reacoop.it)
JS-GIS homepage: http://jsgis.sourceforge.net/
WebStaticMapper homepage: http://www.reacoop.it/wsm

Credits

My thanks go to the following:

• SourceForge.net for hosting this project;
• Dan Steinman for having started the Dynamic Duo cross-browser tutorial & API;
• the Web Design Group for the great tutorials on HTML and Cascading Style Sheets;
• the GNU project and the free software foundation for all the work they did and they're currently doing.

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JS-GIS © 2001, 2002 by Luca S. Percich (mailto:luca.percich@reacoop.it)
Last updated: dec 26, 2002