Spatial search

The Location module has a 'proximity' argument.
I have factored that out in a separate argument handler. You can find it here[#1171232-5]
You can use www.example.com/my_page/london_20 .
It shows everything in as 20x20km square, or a circle area.

@pinkonomy, can you try that? ATM it is part of Geolocation field, but I am happy to make a variant for GMap module.
The patch is still homeless.
@podarok, would this fit in GMap module?

This patch only searches the locations in your own Drupal Database. Is that what you want? Or do you want to read Google data?
IIRC, GMap already offers a 'filter' (instead of an argument/contextual filter), where you can add the radius.
Your example shows some nifty JS. I'm not into that.

You might want to check out Geolocation Proximity. It works with the Geolocation field type, but lacks support for Location/Addressfield/..

OTOH, perhaps you can load all nodes, and set the AutoCenter/Center property somehow.

Another option, using Geofield: #1469956-89: [Meta] - Improve Views-powered Geofield proximity searches