If the area in question is a field or garden, it might be possible to work out its area without leaving your computer. Once the area is displayed on-screen, click Tools, Ruler and select the Path tab. Click around the perimeter of the area until its shape is defined. On each click, the length ofthe current section is displayed on-screen. Make a note of each figure.

With the perimeter of the area defmed, click on the Line tab in Google Earth's Ruler box, then split the defined area into triangles by using the red squares around the perimeter as nodes for the triangles. The length of each side of every triangle is displayed as it is drawn and the choice of units is up to you - anything from centimetres to miles. Jot down the lengths ofthese sides as you measure them. It may be advantageous to print the map to make this easier.

For internal measurement and in situations where Google Earth shows insufficient detail, draw a rough plan of the area and split it into triangles, then measure the actual physical dimensions of each triangle using a tape or laser measure and transfer them to the plan. Once the measurements have been made, start Excel and on the blank worksheet.



The formatting of the headers is up to you, or you can leave them as they are. Once they're in place, use the computer-generated or hand-drawn plan to fill in the lengths of all three sides of each triangle: one triangle to each row of the worksheet. For simple shapes, there might be only two or three triangles, but complicated shapes could require many more. At this stage, it would be advantageous to label the triangles with letters of the alphabet, both on the plan and on the worksheet, to make them easier to track.

Oddly enough, Excel has no built-in function to calculate the area of a triangle, but it's easy to create a formula. In cell D2, type =SUM(A2:C2)/2 and then press Enter. To copy this formula into the cells beneath it, click on cell D2 and then place the mouse pointer over the black square in the bottom right-hand comer of cell D2. Drag the square downwards until every row containing a triangle has been selected, then release the mouse button. In cell E2, type the formula =SQRT(D2*(D2-A2)*(D2-B2)*(D2-C2)). Press Enter and then copy it downwards in the same way.

Type the label 'Total Area' into a cell in column -. D (we used D14) and press Enter. All that then remains is to add up the areas ofthe individual triangles to arrive at the total area of the irregular shape. In the 'cell to the right of the 'Total Area' label, use the fom1Ula =SUM(E2:EI2), where 2 and 12 are the row numbers of the first and last triangles in the list. Press Enter after typing in the fomula.