Below is a map that indicates all the locations in the world where we need to place a Chamber of Eternal Light. (This does not preclude you from placing a Chamber of Eternal Light elsewhere, such as in your home, which may not be in one of these locations.) Please note, while Lantos said we need to place 7,000 Chambers of Eternal Light around the world, they are to be placed in major population centers. Therefore, the number of Chambers of Eternal Light to be placed in a major population center will be significantly greater than would be required just for that city, since that location must also house Chambers of Eternal Light for surrounding rural areas. For example, while Tokyo, Japan does not actually require 155 Chambers of Eternal Light for itself, it is the world's most populous metropolitan area, and as such will house many more Chambers of Eternal Light than would be required by its population alone.
You may click on a blue dot, and it will bring up an information badge, showing the number of Chambers of Eternal Light needed, the city and country, the altitude and the population density of that location.
If a location has many Chambers needed, it will be represented by a circle with a number inside it. You can zoom in to that location to see the individual locations.
To zoom in or out, you can use the + and - buttons on the top left of the map, which become visible when you place your mouse over the map. You can also use the zoom-to-location button (the top button) in the top-left of the map--just click that button, then click-and-drag your mouse over an area you'd like to see in greater detail.
To move around the map, just click-and-drag with your mouse.
To reset the map (and start over), simply reload the web page.