An object that is to be achieved by the present invention is to provide an azo pigment having excellent transparency, suitable dispersibility, and a low viscosity, an ink, and the like. An azo pigment according to the present invention has a zeta potential of 80 to 30 mV in isopropanol (IPA). The content of a metal element in the azo pigment is preferably 0.05 to 2.00 parts by mass relative to 100 parts by mass of the azo pigment. The metal element is preferably an iron element. The ratio (Fe/C) of the concentration Fe (atomic %) of an iron element in the surfaces of particles of the azo pigment to the concentration C (atomic %) of a carbon element in the surfaces of the particles of the azo pigment which are determined by X-ray photoelectron spectroscopy is preferably 0.20 or less.

Embodiments of the present invention provide a computer-implemented method for assigning identifiers to geographic locations within digital map data, comprising selecting a region within the map data, dividing the region into a first plurality of cells each uniquely addressable by an identifier of a first length, selecting a portion of the region and dividing the portion into a second plurality of cells each uniquely addressable by an identifier of a second length, wherein the second length is shorter length than the first length and a geographic location within the portion of the region may be uniquely identified by an identifier of the first length and an identifier of the second length.