Software strategy: online maps: programs serve up geospatial data through Web browsers

CADalyst, Feb, 2005 by James L. Sipes

THE EMERGENCE OF WEB GIS has greatly changed the way we access mapping information. The Web is becoming a portal for GIS functionality and data distribution, primarily because it's the most cost-effective way to reach a broad audience and give it access to geospatial data. Broadband Internet connections are fast enough to download even massive amounts of geospatial data.

The biggest benefit of Web GIS applications is that they allow maps to be displayed and queried with any standard Web browser. Applications can access Web services through Web protocols such as HTTP and XML, and users don't need to worry how the application was created. They just know that they can sit down at their computer, fire up their standard Web browser and find the maps they need.

Popularizing GIS

It used to be that only technical gurus could use GIS, but that has changed significantly in recent years. Many GIS users today probably don't know the difference between a shape file and a coverage file, and frankly, most probably don't need to. They simply want to access geographic data, assemble it in ways that address specific questions and then see maps that show the results. For example, a couple moving to a new community may want to know where all libraries within a 20-mile radius are located, or a motorist may need to know the quickest way to get from one side of a city to the other.

These types of users typically are not worried about where the data came from, who created it or where it's stored. They just want to be able to log onto the Internet and use their browser to find the answer.

Standards

The development of standards such as OpenGIS that encourage openness and interoperability has made it possible to build, access and exchange GIS data across different platforms. SOAP (simple object access protocol), Microsoft .NET, J2EE and XML (extensible markup language) are just a few of the common standards that underlie Web-based GIS. Applications based on these standards are platform independent, nonproprietary and scalable without loss of quality across various devices.

Early last year the OGC (Open GIS Consortium) introduced a major new initiative to develop and enhance standards that make it easier to develop and access geographic data via the Internet. The Web-oriented standards that OGC is focusing on include a common architecture, user-defined workflow, information interoperability and location-based services. The OGC is also developing compliance tests for and improving Web-oriented OpenGIS specifications.

Strategies and Tools for Web Mapping

Many strategies apply to creating a GIS Web mapping application. Some general tips to consider include:

* Build your application on open standards because this will provide the greatest flexibility in the long run.

* Publish data in its native format when possible and avoid using translators or other techniques that require the creation of additional copies of data.

* Increase flexibility by ensuring that the Web mapping solution can link external database tables to spatial layers and objects.

* Provide intelligent data to users and allow them to make their own decisions on how to put it together.

* Allow users to add their own data.

* Ensure that the application is scalable, meaning that applications can work on slow networks as well as faster networks with broader bandwidth.

* Select the right tools for the job.

Not all GIS Web mapping tools are the same, and different developers use them in different ways. They range from those that produce static and dynamic map images to more advanced programs that tap into real-time data. We are seeing more and more integration of spatial databases that can be updated in real time with remote sensing, GIS, GPS, telecommunications and interactive interfaces that allow users to access all this information while sitting in front of their home computer.

In the simplest Web GIS application, a browser is used to request information. That request is forwarded to a Web server that passes it on to a GIS server. The GIS server generates a graphic file, and that graphic file is sent back to the Web server so that the user can see the results. This is an effective way to look at maps, but users typically must select from the options that are provided. They don't have direct access to the GIS data and therefore can't ask their own questions. The United States Census Bureau's Tiger Mapping Service is an example of this type of map generator. It lets users build a custom map for any location in the United States in a matter of minutes.

The two products that are among the most prominent for creating Web mapping sites are Autodesk's MapGuide and ESRI's ArcIMS. MapGuide features a highly scalable server built for network environments and a customizable viewer API (application programming interface).

The City of Vancouver's VanMap Web site uses Autodesk MapGuide to help pull together geographic data from a range of sources and make it available in GIS format to city staff as well as residents. Users can navigate through a variety of maps and access information about the city's infrastructure.