Adding transparent overlay on google map

I was looking at apartment listings when I came 开发者_开发问答across this,

And I am wondering how it is achieved?

EDIT:

Found the image overlay using inspect element. Question is, is there an api to do things like this?

You can implement a custom map type with the help of the ImageMapType object. You can implement it to returned a darkened/half-transparent images for the map tiles. You can then overlay this map type over the normal one like so.

The answer would be no. There's no API for adding fixed images over a google map. Why? Because it's the standard behavior for any div (if you want to mimic what they did, just put a div after the map div and position it absolutely...in this case top:0 and left:0 with 100% width and a gradient or static image as a background). You can place any div over any other div, even if it contains a google map. Now there are api's for placing items INSIDE the map...these drawings can be just about anything, but they require a lat/long boundary because they are inside the map. There are also map controls you can place on the map....similar to a fixed div, BUT it has a certain flow inside the map, so if you have a map terrain dropdown and you click it, if that dropdown overlaps another map control, that map control will move down.