Visualisation of Point Scale: The Tissot Indicatrix
Consider a small circle on the surface of the Earth centred at a point P at latitude and longitude . Since the point scale varies with position and direction the projection of the circle on the projection will be distorted. Tissot proved that, as long as the distortion is not too great, the circle will become an ellipse on the projection. In general the dimension, shape and orientation of the ellipse will change over the projection. Superimposing these distortion ellipses on the map projection conveys the way in which the point scale is changing over the map. The distortion ellipse is known as Tissot's indicatrix. The example shown here is the Winkel tripel projection, the standard projection for world maps made by the National Geographic Society. The minimum distortion is on the central meridian at latitudes of 30 degrees (North and South). (Other examples).
Read more about this topic: Scale (map)
Famous quotes containing the word point:
“Some parents feel that if they introduce their children to alcohol gradually in the home environment, the children will learn to use alcohol in moderation. I’m not sure that’s such a good idea. First of all, alcohol is not healthy for the growing child. Second, introducing alcohol to a child suggests that you condone drinking—even to the point where you want to teach your child how to drink.”
—Lawrence Balter (20th century)