Mapping "fuzzy" neighborhoods
February 16th, 2006 by JTJ

The good folks at Directions Magazine  turned up this interesting mapping report.  Be sure to drill down into the explanations for the “fuzzy line” and the “blobby” algorithm concepts. 

“The algorithm for drawing neighborhoods is the “blobby”
algorithm, well known in computer graphics. You can think
of each point in a neighborhood as a little magnet, and the
neighborhood is the region where the combined attraction of
all those magnets is above a certain strength. A single
point makes a small circle on the map. The influence of a
number of nearby points will combine to make a curved blob.
Read more about blobbies:

This is one of the first references I've come across using the concepts of the mathematical idea of “fuzzy logic” applied to geography.  Perhaps some readers can point us to similar examples.

“The Neighborhood Project
compiled by Nora Parker, Senior Managing Editor 

Chisholm and Ross Cohen are working on a project to define neighborhood
boundaries, so far only in San Francisco, but eventually in other
cities as well. (If you get impatient and want to launch
this project in your city, they suggest you can download the software
and get busy.) Neighborhood boundaries? What does that mean? Generally
neighborhoods are not defined by exact boundaries – they are defined by
what geographers call “fuzzy lines” – lines that are not well-defined.
(An example of “fuzzy line” might be the line between two bioregions.
These are generalized, mappable regions, that might involve factors
such as precipitation, soils, topography, etc., but there is no defined
on the ground when you cross from one region to the other – the change
between regions is more gradual. This contrasts with the line between
two countries, for example, where you might literally be able to stand
at a border crossing with one foot in each country, or even closer to
home, the line between my neighbor's property and mine.)  The Neighborhood Project
is an excellent illustration of the concept of fuzzy lines – if you go
to the site and look
at the map, you'll note quite a bit of fuzziness to the neighborhood
definitions. You can even begin to perceive it in the very small scale
map included below. People living next door to each other might
consider themselves to be in two different neighborhoods.

The site uses housing post data from craigslist, which includes addresses and neighborhoods, as well as a public poll on the site, to
generate address/neighborhood pairs. Open source products (, Python and PostgreSQL) are used to geocode and map the data.

Neighborhood Project's map of San Francisco. The dots are colored based
on what neighborhood residents considered their “home.” Used by
permission. (Click for larger view.)

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