One of the challenges I faced in developing Wikitree's Percheron Immigration Movement project was fullfillling my desire to visualize the location of origin of the 300-odd Percheron pioneers who immigrated to New France. The project has involved developing standardized profiles of Percheron pioneers culled from reputable lists available from Gervais Carpin's thesis as well as from the 2 lists at perche-quebec.com and perche-canada.net websites. I eventually elected to realize this mapping visualization by using a cartodb.com bubble map as background layer then using Paint to manually define 17th century villages along with the number of pioneers for each village and associated notes, title and background layer masking.
The end product is the map shown at http://www.wikitree.com/index.php?title=Category:Percheron_Immigration
, which is consistent with the Carpin-number-centered wikitable immediately below and, futher below, the alphabetical list inherent with the Percheron Immigration Category derived from profiles.
While more labor-intensive than can be made from Google Maps, the cartodb.com approach is the only one I know of that caters for bubble size related to number of profiles for any given location of origin.
It appears that cartodb.com is free for colour-based sub-layers involving no more than four colours, where I show three sub-layers or colours in my case.