# How to calculate difference between bounds in Google Maps?

Is it possible, after "bounds_changed" event, to get polygon coordinates covering the difference between new bounds and previous bounds?

Any idea how to do it? Any help would be greatly appreciated.

getBounds() returns a LatLngBounds object that supports equals(), intersects(), contains(), etc.

• `intersects()` returns boolean value while `union()` returns `LatLngBounds`. So `intersects()` is not so useful. – Xyroid Jul 18 '17 at 9:07

As I am sure you are aware the `bounds_changed` event occurs after the bounds have changed, therefore the previous bounds are "lost".

I would approach this by having two global variables called `prevBounds` and `newBounds`. Then, within my handler for the `bounds_changed` event I would do the following:

1. Set `prevBounds` equal to `newBounds` which will give me my previous bounds
2. Set `newBounds` equal to the map's current bounds which will give me the new bounds

After the `bounds_changed` event I would have two variables; one containing my previous bounds and one containing the new bounds of the map. Then you can calculate the difference between them.

• Yes, I know that. I should be more clear in my question. What I wanted help with is this actual calculation between new and previous bounds. I suck at geographic calculations... Anyway, thank you for your answer. – Arek Aug 31 '12 at 11:32
• @Arek I see what you mean now, so what do you actually want to calculate the difference of? Width, Height, Area? Of course if the bounds changed because of a pan then there will be no change in size, just location - what difference would you want to calculate in that case? – CHenderson Sep 1 '12 at 10:48
• Maybe it will be best explained with an image. What I need is the coordinates of the green area. – Arek Sep 3 '12 at 6:28