cql_filter

CQL (Common Query Language) filter is a query language used in Geospatial Information Systems (GIS) to filter and retrieve specific data from a dataset based on certain criteria. It is commonly used in mapping applications and geospatial databases.

CQL filters allow you to define queries using logical expressions and comparison operators to select features or objects that meet specific conditions. These filters can be used to query attributes, spatial relationships, or a combination of both.

For example, a CQL filter can be used to retrieve all the cities within a certain distance from a given location, or all the buildings with a specific height range.

The syntax for a CQL filter is typically written as a string and can vary depending on the GIS software or database system you are using. It usually consists of attribute names, comparison operators (such as "=", "<", ">"), logical operators (such as "AND", "OR", "NOT"), and values.

Here's an example of a CQL filter in the context of searching for cities within a specific distance:

distance(geometry, POINT(x, y)) <= radius

In this example, `geometry` represents the location of the city, `x` and `y` represent the coordinates of the center point, and `radius` represents the maximum distance from the center point.

I hope this helps! Let me know if you have any more questions.