NUMBERING SYSTEM OF INDIAN TOPOGRAPHICAL SHEETS

Survey of India , a department under Ministry of science and Technology of Government of India located at Dehradun is prepare topographic maps. The maps are in 3 different scales: 1: 25,000, 1:50,000, and 1: 250,000. All maps represents some particular area and these are prepared from the top of the map towards north so that study of the map is easy. All the maps are numbered and this system of sheet numbering by Survey of India is called “India and Adjacent Countries series.” Each series is numbered to help to locate the areas or places.

For the purpose of an interaction series (within 4⁰  N to 40⁰ N latitude and 44⁰ E to 124⁰ E ) at the scale oaf 1:1,000,000 is considered as a base map and this map is called million sheet map. The million sheet map which scale being 1:10,00,000 ( 1cm to 10 km) or1:M each covering 4⁰ of longitude and latitude .  The numbering of sheets in India is based on the number system of maps of india and these series bears the numbers like 1,2,3,4 …upto 136 consisting of the segments that cover only land area. these 136 such sheets cover India and adjacent countries and these numbers are known as index number of the area.

For example , sheet number 79 is consider for further discussion. Its extension is from 24⁰ N to 28⁰ N and from 90⁰ E to 94⁰ E . Fig:1

The million sheet has been sub divided into 16 sections(4 row and 4 column), each of 1⁰ latitude x 1⁰ longitude and each part is numbered with block capital letter of English alphabet A to P. the sections start from North West directions, run column wise and end in South East direction. Fig: 2

As the extension of each section is 1⁰ latitude and 1⁰ longitude the scale of this sheet is 1 inch to 4 miles or 1: 250,000. The numbering of one o the sheet is 79 N and its extension is from 26⁰ N to 27⁰ N and from 93⁰ E to 94⁰ E

The 1⁰ x1⁰ sheets are further sub divided into four parts which is known as half inch sheet , each of 30/ latitude and 30/ longitude and the scale is 1 inch to 2 miles or 1: 125,000 . these are identified with the help of cardinal direction NE, NW, SE, and SW. let us take the figure number 3. It is extended between 26⁰ 30^/ N to 27⁰ N and from 93⁰ 30^/ E to 94⁰ E .

 Fig: 3

The 1⁰ x1⁰ sheets can also divided into 16 equal part or sections, numbering from 1 to 16 in a column and each of 15^/ latitude and 15^/ longitude. Each part will have a scale 1inch to a mile or 1:63360 or 1:50,000.
                                       

                            

Fig: 4

This is also known as 30^/ x 30^/ (Scale 1:100,000) one inch map and this is the most common type of map produced by Survey of India . the extension of the sheet is 79 N/14 and is from 24⁰ 30^/ N to 25⁰ N and 93⁰ 15^/ E to 94⁰ E.

The 1 inch sheet (15^/ x 15^/) can be divided into 4 sheets. Each of 7 (1/2)^/ and are numbered as NE, NW, SE, and SW.the scale of this sheet is 1:25,000 or 1 inch to ½ mile.  This sheets are not very much common in use.  

                                              

 Fig: 5