Question

I have a web application that needs to display 30,000 markers on a map at the same time. I don’t want to use any kind of clustering. I need them to all be displayed.

I also need them to be clickable. The user can click on each point and a popup will come up with information about that point. Even at a low zoom level when there are thousands of markers in a single 256×256 square, the user needs to be able to click on them. It may be cumbersome for the user to click on a point thats bunched up with hundreds of other points, but if there happens to be one marker in the middle of nowhere, I want the user to be able to click on it right there instead of having to zoom in.

How do I do this? I know it’s possible because I watched a video on google video where this guy creates a GTileLayerOverlay app that had clickable markers. He didn’t explain how it was done though.

Is my only option to just remove the GTileLayerOverlay at high zoom levels and replace it with a true GMarker layer? I really don’t want to do that. It seems over engineering to me.

If you were me, how would you go about this?

Answer 1

I found this example is in the Google Maps API Demo Gallery:

Clickable Tile Layer
This example creates a custom map type (GMapType) that shows regional borders and squares for county centers. When the squares are clicked, an info window opens with information about that county. The clickability is accomplished by passing in information about clickable pixel bounds in the cookies attached to the tiles, and doing a client-side check on mouseover for whether the mouse position was within the pixel bounds.

Here’s some commentary on his method.

I don’t have any experience with GTileLayOverlays, but I believe it is possible to accomplish what you’re trying to do without using GMarkers.

Would it be possible to utilize clustering if each cluster could bring up a list of the markers it represents? It seems like having 30,000 markers visible at once would be visually confusing and difficult to navigate .