I have a project in QGIS where one of the things I need to do is work from a police data file with 9 months of crime information, linked to details of county population (age, employment, etc) to report the % of different crimes in each county (7 counties). When I follow the example screenshot given, word for word, to work out a %, I get an message which says: "An error occured while evaluating the calculation string.".
I'm not sure where i'm going wrong. Any guidence would be a lifesaver.
Best Answer
The equation for the field calculator should simply be something like:
(FIELDNAME_1 / FIELDNAME_2) * 100Where FIELDNAME_1 = the field with the number of a particular crime and FIELDNAME_2 = the field with the total number of crimes.
Remember that the data should be stored as numbers. If its as a string bad things will probably happen (possibly the reason for your error).