Interpretation of SOI topographical map: Identification and Marginal Information

 Interpretation of the survey of India (SOI) topographical map requires careful study of the map and the conventional symbols. 

Quality of the interpretation depends on the theoretical knowledge of the geographic features (topography and landforms, Jane, age, System, transport and communication and settlement etc) and their inter relationship and a prior knowledge about the area under study. 

Before proceeding into the interpretation of the map, it is necessary to identify the topographical Map by its marginal information. 

Marginal information of survey of India topographical maps: 

1. Administrative identity: Each SOI topographical Map represents a portion of an administrative area (District of a State) and the  name of the district and state is mentioned in the top of the map. 

Name of the state is written in the middle part of the top margin of the map and the district name is written on the top left margin of the Map (see below image)

2. Index number/ reference number/ sheet number: As the topographical maps are drawn systematically for the entire country (here India), which is subdivided into different spatial units at different levels and maps are drawn for each smallest spatial units for the entire country. Thus each map contains a unique identification number which is known as index number/ reference number or sheet number of the Map. 

3. Map legends or Keys: Map legends or keys for the conventional symbols are the most important part of any map and for topographical map. It is even more important because identification of the geographic features and their characteristics entirely depends on the conventional symbols and their meanings.  

In the survey of India topical maps, the conventional symbols are displayed in the left and right part of the bottom margin. 

4. Scale

4. Scale: without a scale, a map cannot be drawn because the portion of the actual earth’s surface has been reduced to a scale and is represented on a map by systematic transformation through my projection. Scale represents the ratio of the Map distance and corresponding ground distance. 

In the topographical Map, the scale is represented in all the three forms of scale i. e. Statement scale, Representative fraction and graphical scale and located at the middle of the bottom margin of the Map. 

5. Sheet index and 6. Administrative index: As it has already been mentioned that the topographical map has been drawn in a systematic way for the entire region and therefore for a particular area several maps are produced each of which has been drawn with unique identification number. 

Thus in the topographical Map, a sheet index has been provided for reference to map readers to provide the additional  information about the other  topographical maps surrounding the concerned map under study. 

In addition to the sheet index, administrative index represents the portion of the area of a particular administrative division, represented in the concern Topographical Map. 

7. Coordinates: Each topographical Map is drawn with the parallels of latitude and meridians is of longitude in order to provide exact coordinate values (positional advantage) to the Map readers.