Design more tiles at locations where density of spectra is low

[schlafly]

We should think about designing more tiles in areas where the density of spectra is low. An extreme example would be designing new tiles at the locations of old tiles here
#88
where we ended up marking all of the spectra as bad, but we didn't retire the tiles, since we unintentionally MTLed them. But more broadly there are a number of locations where we ran with an incomplete focal plane, and we could consider preferentially adding tiles in those locations to bring them up to nominal density.