📖 PART 1: Introduction to Topographical Maps
A Topographical Map is a large-scale, detailed map that shows the three-dimensional
features of a landscape — hills, valleys, rivers, forests, roads, settlements — on a two-dimensional
surface, using contour lines, conventional symbols, and colours.
- Published by the Survey of India (SOI). Scale used is typically
1:50,000 (2 cm = 1 km) or 1:25,000.
- Every topographical sheet has an Index Number (e.g., 53A/4) to identify it.
📍 PART 2: Grid Reference System
Four-Figure and Six-Figure Grid References
- A topographical map is divided into a grid of numbered vertical lines
(eastings) and horizontal lines (northings).
- Four-figure reference: Identifies a grid square. Read the easting (left to right)
first, then the northing (bottom to top). E.g., 2534 means easting 25, northing 34.
- Six-figure reference: Pinpoints a feature within a grid square. Divide each grid square
into tenths mentally. E.g., 253348 means easting 25.3, northing 34.8 — locating an exact point.
💡 Memory Tip — Grid References
Always read
along the corridor (easting), then up the stairs (northing). Eastings first,
northings second. "Along the hall and up the stairs."
🏔️ PART 3: Contour Lines
Definition and Properties
A contour line is an imaginary line on a map connecting all points at the same
elevation (height above mean sea level). The vertical distance between two consecutive contour
lines is called the Contour Interval (CI).
- Contour lines never cross each other (except in overhangs — rare).
- They are always closed curves (they close on themselves, even if not visible on the
sheet).
- Where contours are close together → steep slope. Where far apart →
gentle slope.
- Every 5th contour (index contour) is drawn thicker and labelled with its elevation.
Landforms Shown by Contours
| Landform |
How Contours Appear |
| Hill / Knoll |
Closed concentric circles (innermost = summit); values increase inward |
| Valley |
Contours form a V or U shape pointing uphill (toward higher values) |
| Ridge |
Contours form a V or U shape pointing downhill (away from higher values) |
| Steep Slope (Escarpment) |
Very closely spaced contours |
| Gentle Slope |
Widely spaced contours |
| Cliff |
Contours merge / touch (near-vertical) |
| Plateau |
Closely spaced on edges; widely spaced (flat) on top |
| Depression (hollow) |
Closed contours with hachure marks (short lines pointing inward toward depression) |
| Spot Height (BM) |
Exact elevation given as a number (e.g., ▲547) |
Relative Height and Depth
- Relative Height = the difference in elevation between two features = (Contour Value of
higher point) − (Contour Value of lower point).
- Relative Depth = depth of a depression = same calculation applied to hollows using
hachured contours.
🎨 PART 4: Conventional Colours and Symbols
| Colour / Symbol |
What it Represents |
| Blue |
Water features — rivers, lakes, canals, ponds, wells |
| Green (shading) |
Vegetation — forests, orchards, scrub |
| Brown |
Contour lines; relief features |
| Black |
Human-made features — roads, buildings, railways, boundaries |
| Red |
Important roads, urban areas (on some editions) |
| Yellow / uncoloured |
Agricultural land / open ground |
- Hachure marks: Short lines pointing into a depression — used to show hollows and
craters.
- Triangulated Height (△): Exact height of a summit determined by survey triangulation.
- Bench Mark (BM): A fixed point of known height marked on permanent structures.
📏 PART 5: Types of Scale
| Type |
Definition |
Example |
| Statement Scale |
Written in words |
"2 centimetres to 1 kilometre" |
| Representative Fraction (RF) |
A ratio with no units; same unit for both map and ground |
1:50,000 (1 cm on map = 50,000 cm on ground) |
| Linear Scale (Bar Scale) |
A drawn line divided into units to measure distances directly |
A ruler-like bar marked in km |
Measuring Distance and Area
- Direct Distance: Use a ruler to measure the straight-line distance on the map, then
multiply by the denominator of the RF (and convert units).
- Area of a Full Grid Square: If RF is 1:50,000, then 2 cm = 1 km. Each grid square is 2
cm × 2 cm = 1 km × 1 km = 1 sq km. Count full squares to calculate area.
🧭 PART 6: Directions (Eight Cardinal Points)
- The eight cardinal directions: N, NE, E, SE, S, SW, W, NW.
- North on a topographical map is always towards the top of the sheet (marked by a North
arrow).
- To find direction between two features: draw a line from the first feature to the second and compare
with North.
🌊 PART 7: Drainage Patterns
| Pattern |
Appearance |
Cause / Terrain |
| Dendritic |
Tree-like branching (like a tree's roots) |
Uniform rock / horizontal strata; most common pattern |
| Trellis |
Right-angle tributaries meeting main stream (like a garden trellis) |
Folded/tilted rocks with alternating hard and soft bands |
| Radial |
Streams radiate outward from a central high point |
Domed hills, volcanic cones, isolated peaks |
🏘️ PART 8: Settlement Patterns
| Pattern |
Description |
Where Found |
| Clustered (Nucleated) |
Houses grouped tightly together around a central point (well, temple, crossroads) |
Fertile plains; areas needing cooperation (farming, defence) |
| Dispersed (Scattered) |
Houses spread far apart across the landscape |
Hilly / forested areas; pastoral regions; poor soil |
🌐 PART 9: Land Use and Natural/Man-Made Features
- Land use shown on topo maps includes: cultivated land (fields), orchards, forests,
grasslands, built-up areas, water bodies, marshes.
- Means of transport: Metalled roads (pucca — black line with white fill), unmetalled
roads (double dashed line), cart tracks (single dashed), pack tracks / footpaths (single thin dashed),
railways (line with cross-hatching).
- Natural features: Rivers and streams, hills, forests, lakes, swamps.
- Man-made features: Buildings, roads, bridges, canals, reservoirs, temples, schools,
post offices (identified using the index/legend at the bottom of the sheet).
📝 Quick Revision – Key Facts
| Topic |
Key Fact |
| Topographical maps published by |
Survey of India (SOI) |
| Standard scale of SOI maps |
1:50,000 (2 cm = 1 km) |
| Contour interval |
Vertical distance between consecutive contours |
| Valley vs Ridge (contours) |
Valley: V-shape pointing uphill. Ridge: V-shape pointing downhill |
| Dendritic drainage |
Tree-like; uniform rock |
| Trellis drainage |
Right-angle branches; folded rock |
| Radial drainage |
Outward from a peak; domed hills / volcanoes |
| Grid reference rule |
Easting first (left→right), Northing second (bottom→top) |
📌 Chapter Summary
- Topographical maps (Survey of India, 1:50,000) show relief using contour lines (equal elevation).
- Contours: close = steep; wide = gentle. V uphill = valley; V downhill = ridge. Hachures =
depression.
- Scale: Statement / Representative Fraction / Linear (Bar) Scale.
- Grid references: 4-figure (square) and 6-figure (point within square). Easting then Northing.
- Drainage patterns: Dendritic (uniform rock), Trellis (folded rock), Radial (domed hills).
- Settlement: Clustered (fertile plains) vs Dispersed (hilly/sparse areas).