Constraining Map Extent

Though sometimes an ArcGIS map service extends the full world, an application that uses this map service will want to restrict the extent to a way smaller extent. In this post, I will be talking about how to achieve this. Check out the application in action. Note that when you pan the map, it "springs" back to the initial extent. And even after you zoom in, the spring is still in effect. So how did I do this is as follows: I created a sub class of the Map class. In the constructor, I added a LOAD event listener. The LOAD event handler adds two EXTENT_CHANGE event listeners, where one of them is at a lower priority to guarantee that it will called last. This low priority listener sole purpose is to get and save the map extent as the initial extent. In addition, the initial scale is computed and saved too. Now, upon an extent change, we check if the initial extent intersects the new extent. if it does, then we compute the horizontal and vertical overlap distance and we adjust the extent in such a way that there is not overlap. we get the "spring" effect for free (cool, eh?) by invoking a callLater. The callLater handler sets a "bounded" extent, thus the spring effect. Now one last thing, we have to make sure we do not zoom out beyond the initial extent. we accomplish this by overriding the extent setter function, where we convert the given extent to a scale value and we compare that to the initial scale. If it is smaller, we proceed by calling the super function, otherwise we just return. Hope you find this post useful. And like usual you can download the source code from here.