Like linear features, areal features can also have regular or irregular geometric shapes . Regular geometric shapes include circle, square, triangle, and rectangle. It is easier to find the area of a regularly shaped feature than that of an irregularly shaped feature. To calculate the area of a feature with regular shape, the appropriate formula for that shape is used. For instance, the area of a square figure is found by multiplying the length by the width (that is, L x W); the area of a triangle is found by multiplying one-half of the base by the height (i.e. ½b x h), and so on.
Regular and Irregular Shapes of Areal Features
In reality most of the areal features we deal with have irregular shape. Examples of such features are lakes, farmland, school compound, Local Government area, state, country, etc. There are a number of ways by which the area of an aerial feature could be calculated manually. Here we will discuss only three of such methods namely:
Square grid method.
Strip or rectangular method, and
The following general steps are involved in calculating the area of an irregularly-shaped figure:
Trace or copy out the outline of the figure on a piece of plain paper or gridded (graph) paper.
Depending on the method you prefer to use, impose a series (grids or cells) of the appropriate regular shape on the figure
Count the number of cells covering the entire figure. (Note: a single square, rectangle or triangle is a grid unit or cell).