Web GIS Gets Flashy

May 1, 2005 By: Jonathan W. Lowe

The Web-browser plug-in known as Macromedia Flash features such strengths as client-side processing, instantaneous interactivity throughout the display, low bandwidth requirements, and the feel of a desktop GIS environment — all without the hassle of installing a plug-in. In addition, in comparison with the more well-known Internet map server products, Flash alternatives are inexpensive. This article reviews the spatial functionality possible with Flash, a few options for deploying such a system, and some organizations that have adopted this approach.

Flash Points

It almost goes without saying that spatial Web sites require graphics for their map displays. Fortunately, Web browsers can display static images such as GIFs, JPEGs, and PNGs, and, though somewhat of an inflexible design, even animated images. Although they display images by default, browser-graphics manipulation and display have always been limited, and so remain a design consideration for spatial Web-site developers. In the early days (mid- to late-1990s) of interactive spatial Web sites, GIS vendors took one (or both) of two general approaches to creating interactive map graphics in Web browsers.

Some, such as ESRI with its MapObjects Internet map server product, relied on core browser image-display capabilities and served Web pages with GIF and JPEG map images. Each time a user clicked on the map image to navigate or identify a feature, they initiated a request for a new map view. The map server received that request, created a new GIF or JPEG map image, and sent it back in a refreshed page. This approach was limited compared with the functionality of a desktop interface, lacking sophisticated navigation features such as draggable panning or rubber-band zoom boxes, as well as most selection capabilities. However, developers could be sure that any visitor to their spatial Web sites would immediately be able to see and use the maps. Though simple, they were reliable. Others, such as Autodesk with its MapGuide product, created its own mapping plug-ins to overcome the core Web browser's limitations. With a plug-in, browser-based maps became more like their desktop GIS cousins, supporting the navigation and selection conventions desktop users had by then come to expect. Unfortunately, the plug-in required first a download and then an installation. Without the plug-in, the site would not work properly. With the advent of inexpensive broadband, many of us have happily forgotten the agony of downloading software over a modem, but at the time, this was a barrier to the adoption of such solutions. There was also the frustration of attempting to install a plug-in on a permission-protected machine.

But times have changed. Those glorious pioneering days have been eclipsed by a new generation of Web browsers with pre-installed plug-ins and such built-in languages as JavaScript.

Most of the GIS vendors who initially deployed their products on core browser capabilities rather than plug-ins eventually extended those products' functionality with JavaScript. Reviewing JavaScript's (dubious) merits as a component of spatial Web sites demands an article all to itself. In brief, JavaScript's inconsistencies across different versions and brands of Web browsers coupled with its ongoing security risks make it, in this author's opinion, a development choice fraught with peril and frustration. To see for yourself, try scripting a rubber-band zoom box that works reliably on Internet Explorer, Netscape, Mozilla, and FireFox. What works on one brand of browser may have a different syntax or behavior on another or is simply not supported.

Unlike JavaScript (at least in theory), a plug-in's browser compatibility and consistency of scripting — regardless of browser — is the task of the plug-in manufacturer, not the application developer. Macromedia Flash is a free Web-browser plug-in that extends a browser's core image-display capabilities by enabling complex animations that respond to user interaction. Flash's rapid and widespread adoption (often by advertisers to build seductive home-page graphics) convinced browser manufacturers to pre-install Flash — since 2000, most Web browsers include the Flash plug-in by default. So, Flash is still a plug-in, but it seldom requires any download or installation by end users. If your browser is a relatively recent version, Flash content will simply display as intended.