To calculate the area, perimeter or length of the different entities, it is necessary to take into account the geometry of each layer. First, ensure that the participant layer has a defined reference system. It is important to remember that when you work with shapefiles and make changes in the geometry, the area, perimeter and length fields are not automatically updated. It is necessary to recalculate the current values after each change.
To start, right-click on the layer and open the attribute table (e. g. lake). Then right-click on the header of the required field (e. g. Area) and select the “Calculate Geometry” tool. Finally, select the geometric property, coordinate system and units you want to use (see Figure 28; area in Acres US).
Practice: Repeat the process and calculate the area in acre for the plant_cover layer.
The same process as described in the previous paragraph can also be used to calculate the perimeter (e. g. in meters) of the layer: you simply have to change from Area to Perimeter in the “Property” section. For polyline layers (e. g. road_network and water_network) only the length can be calculated (e. g. in meters) and for point layers only the XY coordinates can be calculated. In summary, the “Calculate Geometry” tool allows the geometry to be calculated, depending on the nature of each layer.
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