st: set minimum neighbors using spmat and idistance

[Lyndsay Boggess <lboggess@gmail.com>]

I'm having trouble creating inverse distance weights on a population of
2054 census tracts. I use the following code in order to create the weights
for only those tracts within 2 miles (a theoretically derived distance
pertaining to travelling to crime):

spmat idistance laweights longitude latitude, id(tract)
dfunction(dhaversine, miles) vtruncate(1/2)

This leaves me with 38 islands, which I think is the problem because when I
try to create spatial lag variables, my variables end up with all values of
zero. Is there a way to force spmat to make sure that each tract has a
minimum of 1 neighbor even if it requires to extend the distance
beyond two miles?

I have looked at
http://econweb.umd.edu/~prucha/Papers/WP_spmat_2011.pdf extensively,
but I still cannot find a solution to my problem, so any help would be
greatly appreciated!!

Thanks,
Lyndsay
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