Officials in Topeka, Kan., wanted to publish local crime information on the city's Web site. So viewers could see where crimes took place and then call up the details, local officials considered using GIS to plot incidents on a map. "[But that approach] seemed expensive to develop, or require a large plug-in for people to download," said Steve Tallen, Topeka's director of information technology. This made it a hardship, especially for users with dial-up Internet connections.

Then one of Tallen's programmers discovered chicagocrime.org, a privately built Web site that uses mapping technology from Google to display crime data pulled from the Chicago Police Department's site.

Using the same free Google Maps application programming interface (API), Topeka's .NET programmer created a prototype. "It was just so easy to put on our Web site, and for people to use, that we stuck with it," said Tallen.

Thus, Topeka entered the world of Web mash-ups.

A mash-up is a Web site that blends functions and data from other sites to create a new application. The word mash-up is derived from a method in the pop music industry whereby a song is created by fusing elements from other recordings. Web mash-up aficionados generally agree that the genre first emerged in early 2005, said John Musser, a Seattle-area technology consultant and creator of ProgrammableWeb, which reports on mash-ups and APIs.

However, many say the first Web mash-up -- HousingMaps.com, which combines real-estate listings from Craigslist.com with Google Maps -- was created by Paul Rademacher, a software engineer who worked on Shrek 2 and Madagascar.

But David Maguire, director of products at GIS developer ESRI in Redlands, Calif., said the GIS world has been using Web mash-ups for five to seven years. More recently, he said, a few well known names got involved in this. "It has obviously generated a huge amount of interest -- and rightfully so."

Mash-ups emerged, Musser said, when Web service operators started offering APIs -- sets of instructions that a programmer uses to access functions from one site on another site. Before then, developers used a technique called "screen scraping" to pull data from different sources -- allowing users, for example, to comparison shop on several e-commerce sites simultaneously

This practice initially irked major Web site operators such as Amazon.com, but they soon realized it was driving traffic their way, so they built APIs as a standard, controlled way for third parties to have access to that service, Musser said, and offered them free of charge. "[Today] there are hundreds of thousands of [third-party] shopping carts out there that are built on top of Amazon," he said. Similarly third-party developers use eBay's API to build business management tools for their merchants.


King Google
Although Musser's Web site lists dozens of APIs that give access to a wide range of functions, plotting data on a map seems to be the most popular mash-up application. Though other developers offer mapping APIs in this recent explosion of mash-ups, so far, Google is king.

Strictly speaking, Topeka's crime statistics map is not a pure mash-up: It draws on only one external Web source rather than two or more, combining the Google Map with internal data. City programmers used a similar technique to create an internal application that city dispatchers use to check where people have obtained burning permits, Tallen said.

"We're excited about how this thing works. I think we're going to be seeing a lot more applications using it," he added.

Among other government organizations that employed Web APIs, the Google Maps-plus-internal data approach is also popular. Steve Moore, Web administrator for Larimer County, Colo., created a sex offender locator map for the Sheriff's