To get the area of a polygon on the map, you need to create a polygon feature within a layer and then add the area to that feature.
For areal measurement, the suggested process is:
- Choose Layer > New Layer
- Choose Edit > Add Feature
- Choose Polygon when asked what kind of feature to add
- Hold down the Option key (alt on some keyboards) and click at any point to create the points of the polygon
- When you have finished your polygon, choose Edit > Add Feature or hit Return on the keyboard to save your new feature
- Choose Tools > Add Area Column
The column will be added to your layer based on the Map Coordinate System.
Note that the Area column that you just added is static and only contains values for the existing features at the time the command is run, so if you expect to add more polygons for measuring, or if you want to adjust the polygons and have the area change, additionally follow these steps:
- Choose Window > Show Layer Info
- Choose the Fields tab
- Select the newly created Area row from the list
- From the gear menu, choose Geometry Functions > Area (this automatically puts geometry.area() in the formula)
- Click OK
- The Tools > Add Area Column function calculates the area base on the current Map's coordinate reference system. Take care when using Live Maps as background, as they look best in the WGS84 Pseudo-Mercator projection, which is highly inaccurate at many latitudes. When using live maps to create static area columns, we suggest switching to a Local coordinate system for your layers (or WGS 84 Lat/Long if your coordinates are in Lat/Long) and then creating the columns.
- The geometry.area() function calculates the area based on Map's coordinate reference system or projection. If your map is currently displayed in meters, the area will be calculated in square meters. If your map is currently displayed in feet, the area will be calculated in square feet, etc.
- To create area information based on the layer's coordinates, you can use geometry.area(1) instead of geometry.area(). The calculations will then be performed in the coordinate system of the layer, instead of the map.
- Use geometry.area()/43560 to calculate the area in acres if it is originally in feet
- Use geometry.area()/10000 to calculate the area in hectares if it is originally in meters