Is there a 'friendly' way to create dot-density maps, where a polygon attribute data defines the number of dots (e.g. 1 dot = 100 ) using QGIS 1.7+? I say friendly because after a couple of hours researching all the alternatives seem to require programming. Maybe I am not looking in the right place. I am already aware of the fTools 'Random Points' feature and it is not what I am looking for.

enter image description here

That is precisely what I am seeking. However every time I attempted to run this function. I received the following:

An error has occured while executing Python code:

Traceback (most recent call last):
File "/usr/share/qgis/python/plugins/fTools/tools/doRandPoints.py", line 118, in accept
self.randomize(inLayer, outPath, minimum, design, value)
File "/usr/share/qgis/python/plugins/fTools/tools/doRandPoints.py", line 210, in randomize
else: points = self.loopThruPolygons(inLayer, value, design)
File "/usr/share/qgis/python/plugins/fTools/tools/doRandPoints.py", line 256, in loopThruPolygons
sExt = sGeom.boundingBox()
AttributeError: 'NoneType' object has no attribute 'boundingBox'

Python version:
2.7.1+ (r271:86832, Apr 11 2011, 18:37:12) 
[GCC 4.5.2]

QGIS version:
1.8.0-Trunk Trunk, exported
  • 2
    Could you give an example of what the output should look like and why fTools does not work for you?
    – underdark
    Commented Nov 14, 2011 at 8:18
  • Sure and thank you for following up! I am seeking to take an attribute like the number of children in a U.S. Census Tract. Instead of displaying the polygons as a Graduated Symbol, I would like to display 1 dot = 100 children. Effective I am seeking to replicate this: link
    – rhodee
    Commented Nov 14, 2011 at 15:29
  • Is your fTools updated? Have you checked with another polygon file? Maybe it's corrupted.
    – underdark
    Commented Nov 15, 2011 at 8:02
  • Hi you were correct. It appears my real data is being converted into strings. I am using LibreCalc and the data columns appear to not retain the attributes I specified. What is your approach to this problem?
    – rhodee
    Commented Nov 16, 2011 at 15:33
  • What do you use Calc for? Consider using Field Calculator instead. You won't have troubles with data types then.
    – underdark
    Commented Nov 16, 2011 at 18:09

1 Answer 1


If this result created using "Random points" is not what you are looking for, you'll have to be more specific about your requirements.

enter image description here


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