I just wanted to know what the units for the radius parameter are. This is unfortunately not documented? Anybody an idea?
It looks like it may not be documented in the api v1 documentation, but it is for v2 api - http://www.yelp.com/developers/documentation/v2/search_api.
From v1 documentation:
Radius to use while searching around specified geo-point. Maximum value = 25. If a radius is not specified, it will be chosen based on the specificity of the location.
From v2 documentation:
Search radius in meters. If the value is too large, a AREA_TOO_LARGE error may be returned. The max value is 40000 meters (25 miles).
It looks like it is in miles for api v1 and meters for radius_filter in v2.