I have a multipoint layer in QGIS with 860 points.
Each points has some attributes value from a join, and I need to use one of those attributes (a column) to draw polylines. I need one polylines for each different value of that column (so 180 polylines)
It's not so easy, because to efficiently convert points to lines (maybe eventually to polygons), you need to have a criteria to link them, either node order, or point cloud form. Examples below.
Let's take 2 sets of multipoints.
Make sure every multipoint entity has a unique ID
Convert them into single points
Case 1 : entities are scattered in "easy shapes" like here. You can use a convex/concave hull or alpha shape to try and recreate the line going around, doing a polygon at the end you can reconvert to a polyline. The problem with this method is that the line might not pass through each points...
Case 2 Entities are sequenced with a ID field in the desired line order, and the software will be able to draw a line going from one point to another in the right order. If they have been digitalized or captured in the line order, you can fill a "Order" field with $id operator and use it to fill in the order field in the QGIS tool.
Should they not be ordered, you might have this :
You can find the answer here
To add some visual:
The lines were created with he plugin Points2one based on the values I used in the representation/style of the points in the image. QGIS version 2.18.11.
The resulting line layer consists of polylines, so in my example the 3 green dots results in one polyline. If your multipoints do consist of multiple elements, you first might to convert your multipoints to single points with Vector > Geometry tools > Multiparts to singleparts.
