What do the ZCTAs with an “XX” or “HH”suffix represent?
The three-digit ZCTA code and an “XX” suffix are applied to a large land area (generally larger than 25 square miles) where we had insufficient information to determine the five-digit codes. The USPS may not provide five-digit ZIP Code delivery service in this area. These are generally rural areas with little settlement; for example, parks, forest lands, and desert and mountainous areas. Smaller areas were generally absorbed into adjacent five-digit ZCTAs, but for larger areas, we did not want to overextend the surrounding five-digit ZCTAs. The requirements for ZCTA delineation state that all census blocks receive a ZCTA code. Because large water features may border many five-digit ZCTAs, it would be difficult to divide up the water features and assign the parts to the five-digit ZCTAs on the land. Furthermore, any attempt to add these water features to land-based ZCTAs, would greatly distort the size and shape of the land ZCTAs, particularly in coastal areas. To avoid these problems,
