Is it possible to show relations (for example traffic flow) between polygons (for example counties) by highlighting related polygons by doing a query on a start polygon using QGIS?

Here is an example: Blue polygons represent counties, delaunay-lines with arrow show traffic flow in one direction and (purple) desire-lines without arrow show total traffic flow.

What im doing so far: Flow lines or delaunay lines (created by aequilibrae plugin for qgis)

currently: flowlines and delaunaylines

What would be nice to have: wish: highlighted single relations

To explain the second picture: You do a query on the green polygon. The result is that related polygons get highlighted by the amount of traffic relations (red for a lot, yellow for not so much, blue for no traffic at all) to the green polygon.

  • How do you manage the information about relations between polygons? I suppose you have some n:m relationship with attributes, eg traffic amount. So step 1 will be to select related polygons, and step 2 to draw the selected polygons color coded according some attribute, and lines between polgygon centroids. I would use memory layers for this. – Detlev Nov 26 '17 at 7:14
  • Relations are stored in a table and a matrix as csv. Each relation has information about traffic flow and two id's: one of start polygon and one of end polygon. So they can be linked by these id's. Can you explain how you would do this with memory layer? – MrXsquared Nov 29 '17 at 19:52
  • I have no idea about highlighting yet, but memory layers was something I saw for the first time in the answer for this question: gis.stackexchange.com/questions/283995/…, which is not so far from yours. I think you will need more items in the SELECT part than the make_line of that answer. You could post same data to play with. It would be nice to see a practical implementation of it. – Marco May 8 '19 at 21:00

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