Soviet topographic maps are non-rectangular sheets based on sheet lines defined by lines of latitude and longitude and numbered in accordance with the nomenclature devised by Albrecht Penck in the late 19th century for the proposed International Map of the World.
The IMW was intended as an international project with many nations co-operating in producing standardised a global map at a scale of 1:1 million. This aspiration was never fully realised, but the Soviet Union later adopted the scheme for ts own mapping.
The basic quadrangle defines the 1:1 million sheet, each spanning four degrees latitude by six degrees longitude. Quadrangles, and sheets, are identified by lettered bands north from the equator and by numbered zones east from longitude 180º. New York, for example, at 40 North and 74 West, appears on sheet K-18. South of the equator the same system applies, with the letters preceded by ‘s’.
Each 1:1 million sheet is sub-divided into four 1:500,000 sheets (from north-west to south-east), labelled А, Б, В, and Г respectively (the first four letters of the Russian alphabet).
The 1:1 million sheets are also sub-divided into 36 1:200,000 sheets in a six-by-six grid that is numbered in Roman numerals from I to XXXVI.
The successive sub-division into sheets at larger scales continues. There are 144 1:100,000 maps to each 1:1million sheet, in a 12-by-12 grid numbered 1-144 (or 001-144).
Each of these 1:100,000 sheets is sub-divided into four 1:50,000 sheets (А, Б, В, Г) and, where applicable each of these into four 1:25,000 sheets (lower case а, б, в, г) which then each sub-divide further into four 1:10,000 sheets (1,2,3,4) . These last two scales were only produced for USSR territory.
The system immediately locates any sheet precisely on the surface of the globe.