Contribute > apps > #pdxhash


pdxhash is a scheme for geotagging locations in the Portland area with a short string made up of numbers and letters. This tag could be used in urls or as a way of storing Portland locations in a database.

pdxhash is based on the public domain geohash algorithm. Geohash takes a coordinate in latitude/longitude and transforms it into an up to 20 character string, like "u4pruydqqvj". The representation is hierarchical, so all locations in the same area are prefixed by the same letters.

All Portland area locations start with the 'c2' in geohash form, so those letters may be safely omitted for points in this area. By adding letters to 'c2', the location defines a more precise area, allowing for the identification of house sized areas with only 4-5 characters. For instance, the Bagdad Theater is #pdx_0fct. This tag could be used in a tweet.

With #pdxhash, privacy is fairly transparent. Longer pdxhashes refer to more specific parts of Portland. Licensing is also not an issue because the algorithm is entirely public domain.

Using a pdxhash to store geographic points also has the benefit of eliminating the need for a spatial database like PostGIS or SQL Server 2008. Basic spatial queries can be done using string operations without the overhead of a geodatabase.

By adding pdxhash tags to street signs and other land marks, the City could enable people without gps enabled smartphones to pinpoint their location and use it for reporting or other social activity.

Targeted demographic (who app is intended for): App is intended for web developers, but the general concept could potentially be used by anyone.

Specific need that is addressed by app: pdxhash identifies locations in Portland with a short alphanumeric string rather than latitude and longitude or other coordinates. Could be used for geotagging tweets or other content.

Anticipated usage (by whom, under what circumstances, etc): pdxhash could be used to by application developers to build Portland web apps without using a geodatabase or specialized GIS application. It could also be used by the general public to geotag locations.

Who and what will be impacted by the app, and how: Good for developers who are not GIS savvy.

How information is presented, that's not presented elsewhere; how it is unique: pdxhash is a specific version of the geohash algorithm which is beginning to be used to identify locations. By masking most of the geohash string, locations in Portland can be identified by only a few characters.

Strengths of the design: Algorithm is free and open to the public domain without any licensing constraints. pdxhash simplifies making GIS applications by removing the complex calculations required when working with spatial data. This approach is also suitable for being used in cloud computing and non relational database applications that require high performance and scalability.

MIT license
rnixon :: June 2, 2010 - 2:31pm

Very interesting!

chrissm :: July 10, 2010 - 10:27pm

How many characters would be required to usefully identify a street sign (intersection)?

Iknuth :: July 19, 2010 - 11:13am

Looks like it could be done with as few or four or five characters.

Springerj :: February 14, 2012 - 1:18pm

This seems like a really useful idea, but obviously requires a lot of participation to really work well.