GeoWeb
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The primary purpose of SRI's GeoWeb infrastructure is to allow Internet users to find data by its geographic location. Data that refer to a geographic location or area are called georeferenced data. Examples include a 3D model of the Golden Gate Bridge, vacation photos of Yosemite taken with GPS-enabled cameras, the menu for Les Halles in Montreal, a historical document or web site on the Vatican, a weather map of the United States, traditional GIS data, or dynamic data such as the location of a cell phone or airplane.

The GeoWeb infrastructure essentially distributes a vast geographic databases across potentially millions of servers around the globe. The structure is massively scalable and builds on the existing Domain Name System in order to encode a hierarchical latitude/longitude location using a standard Internet URL, e.g. http://3e7n.100e120n.geo/.

GeoWeb cell server hierarchy

Essentially, we segment the planet into a hierarchy of Web servers. Each server in this hierarchical organization has a DNS name that represents a given geographic area of the earth, called a cell. The server is responsible for all metadata about data that lies within this area and has a footprint within a limited range. By limiting the area and range of details in this way, each server becomes responsible for only a tiny fraction of all of the metadata available around the globe. Furthermore, by using DNS names that represent the geographic service area of the server, clients can immediately determine which server to query without the need for a global name server.

In the example above, we have assumed a hierarchy of domain names of the form minutes.degrees.tendegrees.geo, though this need not be the only structure. As a placeholder for the .geo top-level domain, we have created the domain dgeo.org. Below are some example GeoWeb addresses and their corresponding geographic extents.

  • The geographic domain name 20e30n.geo identifies the 10-degree x 10-degree cell whose southwest corner is located at 20 degrees east, 30 degrees north.

  • The geographic domain name 2e4n.10e50n.geo identifies the 1-degree x 1-degree cell whose southwest corner is located at 12 degrees east, 54 degrees north.

  • The geographic domain name 11e21n.3e7n.30e10n.geo identifies the 1-minute x 1-minute cell whose southwest corner is located at 33 degrees, 11 minutes east and 17 degrees, 21 minutes north.

The latitude and longitude gridding of the earth works efficiently for most of the earth, but may break down somewhat at the poles, where a 1-minute server would provide much higher ground resolution than a 1-minute server at the equator because of the convergence of the longitude lines. We will therefore provide northpole.geo and southpole.geo domains for data at all levels of detail within 10 degrees of the poles. These would be the only exceptions to the general minute.degree.tendegree.geo naming convention.

One important advantage of this approach is that all cell servers can initially be located on a single machine. As the project progresses, cells can be moved to different machines in a hierarchical fashion with no change required in the clients. For example, the cell servers for 10-degree cells over the ocean may very well remain on a single machine, while those for the continental areas, which already have a lot of readily available data, may move to different machines early on.

 

 

Copyright ©2001 SRI International. All rights reserved.

For more information, please contact: digital-earth@ai.sri.com.
Last updated: Wednesday, 24-Oct-2001 00:23:06 PDT.