In order for iTopography to compute the area of a surface, the user has to move in a clockwise or a counter-clockwise direction on the boundaries of the surface. Although a polygon can approximate any surface (even a circle), it is wise the corners of the surface to coincide with some of the corners of the polygon. Therefore, if you have a surface that comprises of straight lines then at the point where two lines meet, you should add a point.
If instead, the surface is circular then you could add as many points as you feel like, to better approximate the shape of the surface. Rule of thumb: Add a point whenever there is a change in the direction.
iTopography provides two methods to add these points: a) The first method uses the GPS device. When the user press on the button "Add Points", iTopography uses the GPS device to obtain the longitude and latitude of the location. b) In the second method, the user is asked to give the position of the point relative to the position of the previous point. Thus, the user is asked to give the distance of this new point from the last point, and the angle of that last point (vertex). This angle is the angle that the lines that connect the new point with the last point and the last point with the second to last point make. If this new point is the second point on the polygon, then the second to last point is the last point of the polygon. Please visit the "Instructions" section for an example.
Once we acquire all the points, iTopography will draw the surface and compute the area and the perimeter.
iTopography has four tabs: In the first tab we see some information about the points, and we can edit these points. In the second tab, we see the surface and we read its area and its perimeter. In the third tab, we can change the units (meter or feet) and we have control on the accuracy of the GPS device. Finally, in the fourth device, we find some instructions on how to use iTopography.