We're almost done with the effect. All we need to do now is add the connectors. This is a simple process using a few Photoshop filters.
Duplicate the Background layer (Layer> Duplicate Layer or Ctrl+J) and move it to the top.

Apply a Mosaic filter (Filter> Pixelate> Mosaic) with a cell size of 16 square.

Activate the new top layer and apply a Median filter with a radius of 8 pixels.

As you might have guessed, we'll now apply a Find Edges filter (Filter> Stylize> Find Edges).

Finally, invert the current layer (Image> Adjustments> Invert or Ctrl+I) and change the blending mode to Screen.
