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Updated Filter (markdown)

herm 2012-02-05 12:10:44 -08:00
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Filter.md

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Each Style-Rule can optionally have a Filter attached. Mapnik walks through all Rules of a Style and checks if it has a Filter specified and if this Filter matches the Object currently rendered. Filters compare an Objects Key-Value Information against the specified rules. When the Datasource is a Postgis Database, the Filter operates on the tables columns, for Shapefiles the Attributes are used. Each Style-Rule can optionally have a Filter attached. Mapnik walks through all Rules of a Style and checks if it has a Filter specified and if this Filter matches the Object currently rendered. Filters compare an Objects Key-Value Information against the specified rules. When the Datasource is a Postgis Database, the Filter operates on the tables columns, for Shapefiles the Attributes are used.
In XML [character entities](http://en.wikipedia.org/wiki/List_of_XML_and_HTML_character_entity_references) are used to construct filters. You can use the following characters to specify value-comparisons: In XML [character entities](http://en.wikipedia.org/wiki/List_of_XML_and_HTML_character_entity_references) are used to construct filters. You can use the following characters to specify value-comparisons:
* Greater Than: `>` * Greater Than: `>`
* Greater Then or Equal: `>=` * Greater Then or Equal: `>=`
* Less Than: `<` * Less Than: `<`
@ -13,6 +14,7 @@ In XML [character entities](http://en.wikipedia.org/wiki/List_of_XML_and_HTML_ch
* Equal: `=` * Equal: `=`
Filters can be combined with the following operators: Filters can be combined with the following operators:
* A `and` B * A `and` B
* A `or` B * A `or` B
* `not` A * `not` A