The vast majority of web mapping today is done with Google maps, and though it is free to use Google's mapping API, any web site using it is limited in the amount of customization that can be done. A company deploying a map application based on Google's API must follow the EULA, and must accept the colors, fonts, and map layers that Google includes in its maps' styles. In order to better understand the path of transition to the more extensible open source alternative, it is helpful to understand the client-server model that goes into displaying the map on the end user's web browser.

There are four layers involved in this model, which has become known as the map stack¹. The highest level, closest to the end user, is the Browser UI, which is a javascript or flash library that is loaded into the users' web browser and is the layer of primary interaction. The Browser UI translates the users' mouse and keyboard movements into different map tile assemblies, drawing elements on the map along the way. This is the level where the Google maps API would normally sit, with Google then providing all three layers below it (mainly at the server level); serving up the actual data. The next level in the model is the Tile Cache, which is simply an interface between outside internet requests and the actual data server. It, as its name suggests, acts as a cache for frequently requested map data to reduce stress on the primary data servers. The next level, the actual Map Server, are the servers that render the raw geospatial data for output. It is at this level that the styling can be controlled via a mechanism very much like CSS. The final level in the model is the actual Geospatial Data itself. The data consists of geometric shapes and their associated coordinates and attribute data. The important take-away message of all of this is that an open source alternative exists for each of these four layers in the client-server interaction model.

Indeed, it seems that companies are picking up on the fact that there is money to be made in rolling custom web mapping applications using these open source alternatives along with a tested and supported hardware configuration. Canadian company DM Solutions Group is one such company, maintaining that the customized application designed to fit a customer's specific need, and not the underlying technology, is what creates value in a web mapping product. Since switching over to the open source MapServer database in 2000, the company has since developed nearly 50% of the entire (freely available) database in response to client contracts². DMSG is only is likely at the beginning of a trend of companies moving to open source alternatives to provide highly customized web mapping solutions.

¹Putting Maps on the Web with Open Source Technologies
²Take Control of Your Maps