Python Geospatial Development - Third Edition

Dealing with the scale problem

The preceding illustration reveals a second problem with the DISTAL system: because the USA including Alaska is over 4,000 miles wide, accurately selecting a 10-mile search radius by clicking on a point on this map would be an exercise in frustration.

To solve this problem, we will implement a zoom feature so that the user can click more accurately on the desired starting point. Because the DISTAL system is implemented as a series of CGI scripts, our zoom feature is going to be rather basic: if the user holds down the Shift key while clicking, we zoom in on the clicked-on point. If the Shift key is not held down when the user clicks, we proceed with the search as usual.

Note

In a real web application, we would implement ...