Natural Area Coding System (NACS)

Why is Another System Needed?

Due to the difficulties of using location references with long character strings, such as longitude/latitude, Universal Transverse Mercator (UTM), U.S. National Grid (USNG), and other georeferences that require more than 15 characters for the resolution of individual addresses, consumers continue to use street addresses to specify locations on most location-based services. But street addresses are inefficient (due to complex and variable character strings), difficult to transcribe (particularly when using foreign characters), and frequently fail when used in automatic address-matching procedures (using address databases with typographic errors, missed or outdated entries, multiple matches, etc.). Most important, addresses are not available to 99% of the locations on the earth surface. Therefore, a more efficient and reliable georeference with a complete coverage of the world is needed.

How is an NAC Constructed?

The NACS unifies the concepts of points, areas, and three-dimensional regions based on the fact that a point location is just a relatively small area or a relatively small three-dimensional region. It employs the 30 most common characters (digits and English consonants), instead of only 10 digits, to produce compact, standard representations of locations called natural area codes (NACs). It is defined only on WGS84 to avoid any variations in geodetic datums.

An NAC consists of three character strings separated by blank spaces. The first character string represents longitude; the second string represents latitude; and the third represents altitude. The system divides the ranges of longitude (from west 180° to east 180°), latitude (from south 90° to north 90°), and altitude (from the earth's gravitation center to the infinite outer space) each into 30 divisions, with each division identified by one character sequentially from the character set [0123456789BCDFGHJKLMNPQRSTVWXZ]. Note that each character in this set can be represented by an integer between 0 and 29. Longitude and latitude are divided uniformly, while altitude is divided using an arc tangent function, such that divisions slowly grow from the limited length of the first division at the earth center to the midpoint in the scale at the earth's surface, to the infinite length of the last division at the limit of outer space.

Each division is further divided into 30 subdivisions, each of which is named by one character in the same sequence. The division process can continue to the third level, fourth level, and so on. The resulting divisions in three dimensions form regions called NAC blocks. The [Page 307]divisions form a set of nested grids called Universal Map Grids. Therefore, a first-level NAC block can be represented by an NAC of three characters separated by blank spaces, for example, NAC: 5 6 H. A second-level NAC block can be represented by an NAC of six characters, such as NAC: 5B 6H HN.

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