I work for a major retailer and my job is to figure out where they want to open new stores. We do this by forecasting potential weekly sales for each potential site sent to us. When we designate our trade areas around the potential site we use block groups. In the past we used to just draw a circle of some diameter around the potential site and called it a day. During that experience we figure out by using block groups to designate our trade areas we can forecast average weekly sales more accurately. Since we have demographic data down to this detail I believe it would be in Business Analysts best interest to create a wizard that can define trade areas by block groups and make it so that automatically designates a trade area that has the smallest amount of land area but the largest amount of population or households as possible.