-------- Original Message -------- Subject: [Qgis-user] Calculate acres From: Marc Bordelon via QGIS-User To: "qgis-user@lists.osgeo.org" Date: Thu Feb 20 2025 04:23:51 GMT+0100
I[ve downloaded version 3.34.15 LTR and created a new shape file. Its still not calculating the acres. The feature has "NULL" in it.
How are you calculating the area? Are you using the field calculator? You access it either from the attribute table or from the tab "Fields" in the layer properties. You can also set an expression in the "Attributes Form" in the layer properties.
Talking about expression. Unless you fetch your vector data from a geospatial database, you need to calculate the area with an expression. There are 2 ways to do that:
function $area
Returns the area of the current feature. The area calculated by this function
respects both the current project's ellipsoid setting and area unit settings.
For example, if an ellipsoid has been set for the project then the calculated
area will be ellipsoidal, and if no ellipsoid is set then the calculated area
will be planimetric.
function area
Returns the area of a geometry polygon object. Calculations are always
planimetric in the Spatial Reference System (SRS) of this geometry, and the
units of the returned area will match the units for the SRS. This differs from
the calculations performed by the $area function, which will perform
ellipsoidal calculations based on the project's ellipsoid and area unit
settings.
Syntax
area(geometry)
Arguments
geometry
polygon geometry object
Examples
area(geom_from_wkt('POLYGON((0 0, 4 0, 4 2, 0 2, 0 0))')) → 8.0
You also need to set your units of measurement in your project settings: Project > Properties: Tab "General", item "Measurements" > "Units for area measurement"
I'm at my wit's end on this. I tried creating a dummy shape file and it give me the same results when calculating the acres.
Also, don't use shape files, use geopackage. Instead of saving hundreds of shapefiles in one or several folders, you save one geopackage with several layers/tables. Think of it like the personal geodatabase from ArcGIS. After you're done with your work, you can always export your layers as SHP. Geopackage is so much better than shape.
-- Tobias A Schula Forestry Expert
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