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Geospatial search

What is geospatial search?

Geospatial search is the use of geographical coordinates to enable searching based upon the "position" of documents. For example:

  • A news item search might enable locating news stories reported for areas close to a certain location
  • A shop search might enable locating stores and retailers located close to the searcher

Enabling geospatial search

Documents in geospatial search collections must have a geospatial location specified through metadata in latitude and longitude format.

<meta name="geo.position" content="-37.4500;146.0833" />

Proximity-based relevance ranking and proximity filtering are insensitive to which geodesic datum is used, but do assume that the origin given to padre and the coordinates applied to documents are expressed relative to the same datum.

If the user-supplied origin is expected to come from a GPS device, the origin will be expressed in the WGS84 system and documents should ideally be marked up according to the same system.

If a document's geospatial position is not specified, that documents position is assumed to be 0,0.

This metadata element should be specified using the standard metamap.cfg. Latitude and longitude are specified in sequence and should be represented in decimal degrees (i.e. not minutes and seconds). Latitude should be mapped to a certain metadata class using a content flag of "2" to indicate geospatial data, and longitude will be assumed to be the next element in sequence. For example, to take the latitude and longitude from the "geo.position" HTML tag, mapping x to latitude and y to longitude:

x,2,geo.position

Note that y (longitude) is not explicitly defined — it is implied by the definition of x. The metadata class for longitude should not be explicitly defined. The classes "z", "Z" or "9" should not be specified as latitude metadata in a metamap.cfg, as this leads to uncertainty in the mapping for longitude.

Latitude and longitude (x and y in the above example) can be displayed as standard metadata using search form "<s:Res>md_x</s:Res>" syntax.

Once geospatial metadata has been defined for documents within the collection, and mapped using the metamap.cfg, the collection should be updated or reindexed. After reindexing, the geospatial data is available for searching.

Query options

The PADRE query processor supports a number of options for geospatial search. These options are mirrored through the public search interface.

origin=<lat>,<long>
specifies origin of search
sort=(prox|dprox)
sort by proximity / descending proximity to origin, not relevance
maxdist=<x>
filter out results that are more than x kilometers from the origin

See also query processor options.

See also

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