Adding drag zoom to the map

Google Maps has a zoom control and the JavaScript API makes use of this control to offer a variety of options for programmers. It is a very useful and easy-to-use control. But there are other ways for zooming; for instance, by drawing an area of interest by dragging a box, so that the map zooms to that area.

This functionality does not exist in the standard Google Maps JavaScript API and any of its libraries; you have to code it. Or, you can make use of the utility libraries, developed by the good guys, at the following link:

https://code.google.com/p/google-maps-utility-library-v3/wiki/Libraries

One of their libraries, KeyDragZoom, is exactly for this zoom functionality, and we will use this library in this recipe. ...

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