[Qgis-user] AREA ATTRIBUTE FOR VECTOR LAYER

[Christine]

Hi Ricardo,
if you want to get a density of school points in each polygon, you may
calculate this in the field calculator. 
Assure, you are working in a projected coordinate sytem. Open attribute
table and choose 'open field calculator'. With the field calculator dialog
open, give a name to a new attribute for school density, choose an
appropriate output field type (probably decimal number, real), output field
length and precision and use an expression pattern like 
 <name of attribute of points count>  / $area 

You get the correct syntax of your  <name of attribute of points count> 
doubleclicking on the field's name under 'fields and values'. Be aware that
$area will have the dimension of the squared coordinate reference system's
measure unit (feet or meters). If you want a density based e.g. on km you
have to devide your area accordingly. 

Regards, Christine






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