Changes between Version 6 and Version 7 of UsersWikiCoveragesAndPostgis

Timestamp:

Jul 21, 2011, 4:32:33 PM (13 years ago)

Author:

bnordgren

Comment:

—

UsersWikiCoveragesAndPostgis

@@ -15 +15 @@
 In general, the ''range'' of a coverage is not restricted to numbers. Given a location, for instance, a "nations" coverage may return a country name which contains that location. This is a common use. The ''range'' of a coverage is not necessarily restricted to "primitive" types either: it can even return another spatial type. This will become important later. The only constraint is that a coverage has the same ''range'' (or set of potential values from which an answer may be drawn) everywhere it is defined. If it returns a "County Name" and a "Population" in one place, it returns a "County Name" and a "Population" everywhere it is defined.
 
-Finally, ''most'' (but not all) coverages may be inverted. Using the above example, users may ask for the set of all locations where "County Name" is "Mineral", or "Population" is 20000.
-
 Querying a coverage for a set of values given a location is called ''evaluating'' the coverage. Querying for a (set of) location(s) given some criteria on the values is given the name ''evaluateInverse'' by ISO 19123. The specifics of how answers are generated for these queries depends on the type of coverage and how the "supporting data" are stored.
 
 As soon as you provide a way to query for an value based on a location (and optionally a time), you have created a coverage. It does not matter how the supporting data are stored, or even ''if'' supporting data even exist. The notion of a coverage is a way to define a ''theme'' or a ''layer'' which produces information without worrying about the details of how that information is produced. The coverage is the tool we use to treat vector and raster data seamlessly.
+
+Finally, ''most'' (but not all) coverages may be inverted. Using the above example, users may ask for the set of all locations where "County Name" is "Mineral", or "Population" is 20000.
 
 == Continuous Coverages ==