I am using QGIS.

  • I have a county map as a single polygon, it has one FEATURE in which one FIELD is Area.
  • I have a grid which also a polygon that divides the county into squares and each grid square is a FEATURE which all have a FIELD called Area.

I want a new vector layer with each grid-square as a FEATURE in which the area of the country falling within that grid square is listed under the Area FIELD.

I keep trying to Clip, Extract and Union and I keep getting an "invalid geometry" error. I know this is fairly straight-forward but I keep stumbling over this error time and time again.

  • 1
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    – Ian Turton
    Sep 16, 2020 at 7:30

1 Answer 1


Invalid geometry suggests that your source data may have some problems with it. One or more of the records has a geometry which is - ironically - invalid. Invalid geometry may be caused by self-intersecting lines, short segments, dangling liens or a whole myriad of other data problems.

Im assuming this is a QGIS question - in which case go to Vector > Geometry Tools > Check validity. Depending upon the output of this tool, will depend on what your next steps will be.

  • The geometry checker shows no invalid geometry or errors and I have run the geometry fixer on it but I'm still getting error messages. This is too hard, QGIS has wasted enough of my time today I am giving up. Thank you for your time. nr_aus, it is appreciated.
    – Craig
    Sep 16, 2020 at 8:37
  • ok no worries, it wont be the tool though, its got to be something with the data. Just need to work out what it is. Double check that the geometry types for both layers are 'polygon' or 'multipolygon'. its possible that one of the source data files has stored the geometry as a line geometry type.
    – nr_aus
    Sep 16, 2020 at 13:46

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