Changes

We want a variable that affects the amount of venture capital only through its effect on agglomeration. More specifically, in the case of thehighest1hull, we want a variable that affects the next periods VC only through its effect on the hull size (given that there is always one and only one hull). Moreover, we will be using city-level fixed effects, so a variable that doesn't change over time -- like the size of the city -- will have no variation to drive an effect on hull size. There are two immediate possibilities, using a size measure involving the TIFs or using the number of locations within TIFs. The points measure has two opposing effects in it: it grows as more startups move into TIFs and it grows as TIFs take up more area. The size measure(s) could be the area of TIfs intersecting last periods hull and the area not intersecting it.  hull area in t = f( hull area in t-1 intersecting TIF areas in t, TIF areas in t not intersecting hull area in t-1). The two measures will have temporal variation as TIF areas vary over time and as hull areas vary over time.