An interactive spatial Web site is an online map that users can pan, zoom, and query with any Web browser. If your organization decides to begin building an interactive spatial Web site today, the first step will be assembling the necessary puzzle pieces. At bare minimum, interactive spatial Web sites need an IP Address, network connectivity, a CPU, data storage space, Web server software, map server software, and a customization language (plus your spatial data, of course!). Setting up each of these components of the spatial Web site infrastructure requires an investment of either time, money, or both, and may not be interchangeable. We’ll look at each in turn.

Hanging your shingle. For an adoring public to find and view your Web site, it must have an IP address and be connected to the Internet. These two elements, though almost too obvious to merit mention, can pose the largest expense of the overall infrastructure. Unless, that is, you are willing to cooperate with other people.

Because of their graphics-heavy nature, the typical spatial Web site requires a fast Internet connection. A T-1 connection costs more than $1,000 per month, not including the expense of running the lines to your facility. Even if this is not cost-prohibitive for your organization, consider that even faster connectivity, such as a 42 - 100 megabit connection, is much less expensive if you’re willing to share. In any metropolitan area, there is at least one company paying the high monthly charges for both a collection of IP addresses and "thick pipes" to the Internet. These companies survive, even prosper, when multiple customers colocate their computers at this one point of connectivity, each borrowing one or more IP addresses, each benefiting from the fast connection, and each paying about $150 per month for the privilege. On the down side, if any one Web site in the group suddenly gets swamped with hits, everyone else’s Web sites will also become sluggish. But if the hosting facility’s managers monitor traffic carefully, this (rare) problem is avoidable or can be mitigated shortly after it begins.

Stocking your shelves. Colocation requires hardware with one or more CPUs and enough disk storage space for operating system software and spatial data. Though fast computers with preinstalled operating systems and vast reserves of disk space are gloriously inexpensive these days (just $500 buys a powerful box), maintaining that system for online service is not so cheap. Maintenance includes ongoing tasks such as conducting security checks, monitoring uptime, and performing upgrades -- a time-sink draining $200 or more per month.

Still sound too expensive? Don’t worry, no need to get off that sharing train yet. Extending the co-location business model to those unable to buy hardware or uninterested in administering systems, many Web hosting companies also provide shared access to their own colocated computers. In this arrangement, multiple users each pay a low monthly fee in exchange for a limited portion of disk space on the same colocated machine. The monthly fee also pays an administrator to keep the system secure and performant. These so-called "shared access plans" usually include Web-based email, ftp access, a secure shell, and a public Web site, and are the standard for many small businesses desiring a simple Web presence.

The monthly charges for this arrangement vary (considerably), usually based on the amount of disk storage space and the data-exchange volumes. For example, a site with 100 static Web pages might fill 25 MB of disk. Each time someone visits a page, the site’s computer sends that page’s text and images across the Internet to the requesting browser. If the average page contains 100 KB of text and image data, then 10 page hits will meter one megabyte of data-exchange. Over the course of a month at a large and/or popular site, data exchange can swell to gigabyte levels. Shared access plans slice and dice both disk access and data-exchange volumes with the aim of balancing their users-per-computer ratios (and turning a profit).

Who’s behind the counter? Because so many businesses now have their own Web sites, plenty of companies offer shared access plans, templates for building new Web sites, and easy migration paths to handle increased demand. Spatial Web sites, however, do not fit neatly into the mainstream Web site business that feeds large providers That’s because interactive spatial Web sites require special map serving software; without considerable demand for the capability, large hosts don’t want to support the spatial needs. So, with the introduction of a spatial component, the list of available Web hosts shrinks dramatically.

Before covering some representatives of the spatial Web hosting business, it’s worth understanding the software behind the interactive spatial Web pages. All Web sites rely on Web server software, the most popular of which is the free, open-source product, Apache (www.apache.org), with a 53 percent market share. Microsoft’s (www.microsoft.com) IIS (at $270) holds second place with approximately 30 percent of the market. As your site’s private traffic cop, a Web server receives requests for Web pages, locates the requested data on disk, and returns a copy of that data to the requesting browser.

In concert, Web servers and browsers know how to exchange and interpret text, images, audio, video, and a growing list of other formats such as XML. But reading and drawing spatial data formats, such as shapefiles, is not currently supported. Instead, Internet map server software makers provide two strategies: home-cooking or browser-beef-up.

The home-cookers enhance the Web server with map server software that draws images on demand and embeds them into Web pages. Each browser request for a new zoomed or panned map view is actually just a bounding box and click location that the map server software interprets, converts to a snapshot, and returns as a gif, jpeg, or png file.

The browser-beef-up strategy is the same as home-cooking, but adds plug-in functionality to the browser. The plug-in knows how to interpret streams of coordinates, transforming the browser into a desktop GIS tool with increased functionality over pure image-based solutions. For instance, browsers enhanced with spatial plug-ins let users highlight groups of features or pan without refreshing the page.

Autodesk’s MapGuide (www.autodesk.com), ESRI’s ArcIMS (www.esri.com), Intergraph’s GeoMedia Web Map (www.intergraph.com/gis), MapInfo’s miAware (www.mapinfo.com), and University of Minnesota’s MapServer (mapserver.gis.umn.edu) all generally fit one or both of the above models, serving maps in partnership with the Web server. All but UMN’s free MapServer cost between $1,500 and $4,500 per CPU. There is also a cost in time of installation: the process of uniting the two software packages (Web server and map server, for any of these five offerings) is notoriously challenging, requiring a breadth of knowledge about networks, Web servers, and programming languages that is often new territory for the average spatial professional.

Stamping your trademark. Wait a minute! What’s this about programming languages? Map serving software usually comes with a template or wizards that create a rudimentary interactive spatial Web site with any collection of spatial data. Once the software is installed, users can quickly establish a page with pan, zoom, and identify tools, all without programming a single line of code. Inevitably, though, a template is inadequate. Typical projects require at least three custom functions. For instance, the specification may demand address geocoding or point-in-polygon functionality. Or the contents of the map may link to the contents of the surrounding Web page’s text. Each different map server product has a different customization strategy, all involving some sort of programming or scripting language(s), from Javascript to Perl, from Visual Basic to Java, all free except for Visual Basic ($450 - $699 per license). In the flow of a request, the Web server calls a program (written in, say, Java) that tells the map server to generate an image, which the Java program then rolls into a Web page it creates on the fly. Other programs such as Allaire’s (www.macromedia.com) Cold Fusion or Microsoft’s Active Server Pages might also be part of the software mixture (and expense accounting).