Geographic Processing

Most geographic applications do more than simply display data on a map. Most provide some sort of selection capability, which identifies what a user clicks on. Some geographic applications perform bounds checking to determine if a location or object is inside or outside of another.

Selection

Prajna supports several different ways to perform geographic selection. The GeoCanvas class provides a getShapeAt method, which determines which geographic shape is displayed at a particular coordinate. Since all GeoShapes may include a DataRecord object, this object may be used to identify each geographic shape.

Filtering

Prajna provides several classes for geographic filtering. The GeoFilter class determines whether a particular geographic coordinate is inside of a particular geographic shape. If you have a set of data, and only want to display the data within a particular country or region, you may wish to use the GeoFilter class or one of its descendants.

Locating a Feature by Name

Locating a geographic feature by name is a difficult problem, with several challenges. Humans rely on context to identify a particular geographic entity - a person discussing a vacation to Paris is likely talking about Paris, France and not Paris, Texas. But a computer cannot easily determine this type of context. Therefore, when you develop a geographic application which tries to identify places by name, you may need to determine which location is the correct one depending on your particular application.

Prajna supplies several different geographic locators, each with different properties and uses. You may wish to use one or more of these when developing an application.

• The EsriGeoFilter uses ESRI shape files to determine the geographic entity. It relies upon the associated data contained in the shape files - specifically, the DBF fiel associated with a particular shape file. It uses multiple EsriReaders to access files, and will select a geographic object from those shapefiles if possible.
• The GoogleLocator uses Google's map lookup service to determine the location. It relies on a Google Map Key, which you will need to provide. In addition, Google's map service limits the number of queries each day, so it is unsuited for high-volume applications.
• The GeoNamesLocator uses the geographic name service provided by GeoNames. It can support higher volumes of queries. However, it may identify too many matches for a particular name, and be unable to discern which is appropriate.