val urban_list1 = List("a", "b", "b", "c", "d")
val urban_list2 = List("d", "b", "d", "b", "d")

assert(overlap(urban_list1, urban_list2) == 0.5384615384615384)

assert(overlap(urban_list1, urban_list1) == 1.0)

assert(overlap(urban_list2, urban_list2) == 1.0)