Preparing Basemaps

What is a Map?

Definition: A map is a presentation of any unit of land on a piece of paper or cloth that can be studied through symbols, measured through scale and located through direction.

Types of Maps

• Guide Map - Road map
• Subject related map - Watershed, drainage, geology etc.
• Trend showing maps - Population growth, reduced water level, water quality maps
• Decision making maps - Cadastral maps, mineral maps etc.

Purposes of Basemap

A basemap is a fundamental map that contains information for those who need to refer to it repeatedly throughout the project or process. In the case of Jaldoots training and as the focus to teach village level land and water resource management planning. A basemap should have following information:

• Village boundary
• Farm land and survey information
• Streams and rivers
• Slope
• Important local land marks within the village
• Settlements
• Roads network and connectivity
• Existing traditional /large water bodies

How to Prepare a Basemap?

There is no single map that contains all of the above information and therefore to prepare a basemap there needs to be two maps such as (1) Cadastral Map and (2) Toposheet which contain the above information. Along with these two maps, there needs to be some consultations with village people to identify and locate important local landmarks that people use to visualise the respective areas in their mind and to communicate to farmers and other stakeholder for an effective water management and planning at village and / or Gram Panchayat level.

Cadastral Maps are available at

• District Land Record Office
• Taluk or Panchayat Office

Contains Information about

• Farm Lands
• Local Roads
• Grazing Lands
• Traverse Land
• Settlements
• Tanks

Toposheets are available at

• Survey of India

Contains Information about

• River and Streams
• Roads
• Contours
• Height Points
• Water Bodies
• Important Landmarks

Process of Synthesising Information from Secondary Sources

• Cadastral maps contain two dimensional information i.e. mostly length and area while a Toposheet contains three-dimensional information i.e. length, area and height.
• There is a need to visualise three-dimensional information by studying contour lines and teaching the meaning of contour lines and how to interpret them and determination of slope directions.
  Scale of both maps is different and due to this the size of a cadastral map is larger than Toposheet.
• There is a need to understand the enlargement of toposheet and the reduction of cadastral maps to make them a similar scale and size.
• Decide a convenient scale so that the map can be of a handy size.
• Study the scale of a cadastral map and Toposheet scale.
• Many different styles are there to describe cadastral maps.
  
  • Such as 1 cm = 80 m; 1 inch = one chain of 33/66 feet etc. To convert this, you need to understand scale conversion.
  • Toposheet scale is mostly represented as 1:50000 i.e. the one centimetre in any direction has an actual size of 500 m.

Length: 1 feet = 3048 meter
Length: 1 meter = 3.28 feet
Area: 1 Ha = 100 m X 100 m = 10000 sq. m
 Area: 100 ha = 1000 m X 1000 m = 1 sq. km
Area: 1 Acre: 10 sq. Chain (66×660 ft) = 43560 ft² = 4047 m²
 Area: 1 Hectare = 2.471 Acre

Enlargement and Reduction of Maps

The enlargement and reduction of maps can be done by the following method:

• Enlargement = increase the size of map and reduce the scale
• Reduction = decrease the size of map and increase the scale
• The Photocopy machine has the predetermined capacity to enlarge or reduce maps.
• Further the machine can do enlargements or reductions based on a determined percentage.
• Once both the maps are of same scale, the next step is to trace all the information from the cadastral map onto a semi-transparent tracing sheet.
• Superimpose and align this tracing sheet on Toposheet through aligning common points and features such as old tank locations, roads any other identical features.
• Then on the tracing sheet draw the following information from toposheet:
  
  • Drainage and rivers
  • Other roads not shown on cadastral maps
  • Contour lines
  • Important landmark features such as temples, hill peaks etc.
• Now a Photocopy of synthesised tracing sheet is taken.
• The map thus prepared is to be verified with the village community with additions and corrections of information taking assistance of the local experienced people.
• Finalisation of map giving proper symbol to each feature.
• Legend is to be prepared as follows on the map:
• Legend should have scale (Ex: 1 : 10000)
• Legend should have symbols (as given below)
• Legend should have direction (North Arrow)
• After giving proper border, basemap is ready for use.

Watershed

• Watershed is a geo-hydrological unit draining at a common point by a system of streams.
• Water divide/drainage divide/ridge line is the line that separates adjacent drainage basins.
• In hilly area the divide lies along topographical ridges or may be a single range of hills or mountains.

Order of Streams

Stream order is a measure of the relative size of streams. The smallest tributaries are referred to as first-order streams, while the largest river in the world, the Amazon, is a twelfth-order waterway. First- through third-order streams are called headwater streams. Over 80% of the total length of Earth’s waterways is headwater streams. Streams classified as fourth- through sixth-order are considered medium streams. A stream that is seventh-order or larger constitutes a river.

Source : Jaldoot Resource Book