http://www.valpo.edu/geomet/pics/geo200/religion/jewish.gif

If you have not heard the term or witnessed the phenomenon in action, Jewish Geography is when American Jews meet for the first time and connect what people they both know. Usually, Jews can successfully discover that they have several friends in common. The American Jewish population is separated by less than six degrees of separation and occupies an extremely small world. One way to explain the closeness of American Jews is through their geographic distribution. It is not unusual for one to assume that it is hard to find the small number of Jews in such a large country. However, this is not the case because Jews inhabit distinct regions, where Jews can be surrounded by fellow Jews.
The Glenmary Research institute constructed a map that shows the Jewish population as a percentage of the total population in each county in the U.S. This map shows Jews are concentrated in New York, New Jersey, Massachusetts, Pennsylvania, Maryland, south Florida, and the Californian coast. Each of these states has only a portion of its area with a proportionately larger Jewish population relative to Jewish population in the entire country. The majority of locations in the United States do not have any significant numbers of Jews or have Jewish populations that are proportionally smaller than the amount of Jews in the entire country. As the areas that Jews occupy decrease, Jewish occupied regions become filled with more Jews, and the chance that two Jews know each other greatly increases. It is more likely that one knows people in his own community. If many Jews live in your community, then it is more likely that you know these Jews. It is true that Jewish individuals tend to live in areas with other Jews, and this makes Jews better connected.
Considering the small number of Jews in the world and in the country, the data on the distribution of the Jewish population shows that Jews flock to only a select group of locations with fellow Jews. There is less of a chance that Jews are outside of the Jewish social network because they are not found in random locations that don’t have Jewish occupants, for the most part at least. This simplifies the game of Jewish Geography because the lack of Jews in isolated areas and their high concentration in only several locations better connects all Jews within America. Geography is only one of the many factors that contribute to creating this phenomenon commonly referred to as Jewish Geography.