Given an image, is it possible to manually draw a graph over it? For example, taking the following image:

enter image description here

I want to manually pick the vertices and draw the edges in a "Paint-like" manner to get, for example,

enter image description here

By manually I mean literally using the mouse to select the vertices.

Any ideas?

Note: This is the "easy" solution to this question, where I intend to build an automatic image processing program. For now, however, a manual solution would suffice.

  • $\begingroup$ Have a look at LocatorPane. $\endgroup$
    – Carl Lange
    Feb 10, 2020 at 21:27

1 Answer 1


enter image description here

There are many ways to do this, modifying, improving my method or doing a completely different thing. My goal here is to show a very basic idea that should give you a start. LocatorPane and Manipulate give means of interactive addition/deletion and dragging of points in 2D plane. The problem is how to add an edge -- there has to be interaction between 2 points. The idea used here is the following:

  • Assume empty initial list of edges
  • Trigger for making an edge is when 2 points become close enough
  • Accumulate such edges and build a graph
  • Jump through various hoops for proper sorting, duplicate deletion, etc.

Let's start from importing image:


defining a function:


Note "Index" property usage, which important, because you need to build edges from indexes of points - not from point coordinates. Read docs on all these functions to understand how it works. r defines distance threshold between the points -- if you go under it an edge will be created. Here is an easy interactive app that uses above function to accumulate edges:


You are adding a point with CMD+CLICK action. Note there are many possible improvements. For instance, optimization for speed. Or "undo" action -- you cal also remove a point with CMD+CLICK action, but this will destroy the graph due to ordering and numbering issues, - so there is no undo for now -- up to you to make it. Cool thing about it is - the graph object is easy to get separately and compute with:

{g, MatrixPlot[AdjacencyMatrix[g]]}

enter image description here

Related Resources

Constructing and Manipulating Graphs


Also take a look at this legacy tool:

  • 2
    $\begingroup$ Very nice! When copying your code that starts with "Clear[edges]", it complains because "i" is not defined so "Show[i,g]" has a problem. Did I miss a piece of code that needs to be run? $\endgroup$
    – Mark R
    Feb 11, 2020 at 0:47
  • 1
    $\begingroup$ Thanks @MarkR, yes I added now definition of i, it is the image. $\endgroup$ Feb 11, 2020 at 1:49
  • 1
    $\begingroup$ Thanks for including the image. I really like this. $\endgroup$
    – Mark R
    Feb 11, 2020 at 2:52
  • 3
    $\begingroup$ This is REALLY COOL, Vitaliy! Can you clarify how this is “connecting” the vertexes with the edges from just touching them together, though? I can’t readily tell, is it from the LocatorAutoCreate->True? $\endgroup$ Feb 11, 2020 at 3:23
  • 1
    $\begingroup$ @VitaliyKaurov very cool stuff, thanks! $\endgroup$ Feb 14, 2020 at 17:06

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