The Projection Explorer web page allows you to experment with different projection methods and parameters and evaluate the distortion each method creates.
On the left side of the screen are the controls for setting the method, parameters, and bounds of the projected space. On the right is the projected data with boxes for additional information.
At the top of the settings panel is an image of the countries of the earth as geographic or "unprojected". The box over the countries defines the minimum and maximum range of the latitude and longitude coordinates that will be used to create the grid. Above the box is a control to chnage the longitude of origin for the projection. Moving this will change the location of 0 for the eastings of the projected data.
Below the geographic map is displayed the current Longitude of Origin and the minimum and maximum range of the latitude and longitude coordinates. The "Go" button will animate the projection by changing the longitude of origin and repainting the projected data. Below this are the controls for the Type (Cylindrical, Conic, Azmuthal, etc.) and the specific projection method. Changing the method will update the parameter controls as the parametes change with each method. Also, many of the projection methods will create extreme values when used outside their intended extent. Because of this, the range of values for the latitude and longitude are restricted to a reasonable value
The distortions are visualized and computed by placing a uniform grid of points over the earth. The grid is spaced at some interval, 5 degrees by default, in both latitude and longitude. Then, the points are projected based on the selected method and parameters. The area distortion represents the percent that the area of each cell has increased or decreased from 100% of the original size. Distance is compueted in a similar way using each segement of the meridians and parallels in each cell. The "Angle" distortion is a bit different and represents the average absolute distortion from 90degrees for all the angles at each point. Absolute distortion is used because some angles may be made smaller while others larger at the same point. The "Distortions" information box displays the minimum and maximum distoration for the selected range of latitude and longitud evalues. Clicking on the projtected map updates the information box in the lower left with the distoration values closest to the point clicked on.