Converting points to lines to polygons and back – SpatiaLite

The goal of this recipe is identical to the previous recipe, but it covers how to perform the process with data in a SpatiaLite database. You will to turn points into lines and lines into polygons.

Not all methods are available; for those that are not available, you can use the previous recipe. It will also work on a database layer; it just doesn't save the results to the database. So, the results will need to be imported to the database after completion.

Getting ready

You need to load a vector layer of points with a numeric ID indicating order, and an identifier of unique lines or polygons that is shared between points of the same geometry. For example, you can use census_wake_2000_points loaded into SpatiaLite with the geometry field called geom.

How to do it…

Using DB Manager Plugin (comes with QGIS and is in the Database menu), the QspatiaLite plugin, or an alternate SpatiaLite SQL application (command line or GUI), the following...