Survey of India (SOI)¶
India's oldest and most authoritative mapping agency — topographic maps, elevation data, and official geodetic reference.
What Is the Survey of India?¶
Established in 1767, the Survey of India (SOI) is the national surveying and mapping organisation of India — the oldest scientific department of the Government of India. It maintains:
- Topographic maps at 1:50,000 and 1:250,000 scale
- National Topographic Database (NTDB) — digital layers of terrain, roads, settlements
- SRTM-based Digital Elevation Model (DEM)
- Geodetic control points (benchmark locations across India)
- Open Series Maps (OSM) — publicly available toposheet series
What Data Is Available for Free?¶
Since 2020, SOI has opened several datasets for public access:
| Dataset | Scale | Format | Access |
|---|---|---|---|
| Open Series Maps (OSM) — Raster | 1:50,000 | GeoTIFF | 🟡 Registration |
| Open Series Maps — Vector | 1:50,000 | Shapefile | 🟡 Registration |
| District Boundary | 1:250,000 | Shapefile | 🟡 Registration |
| DEM (elevation data) | 30m resolution | GeoTIFF | Free via SRTM |
SOI Open Data Policy (2020)
In 2020, India's Geospatial Data Policy allowed SOI to release 1:50,000 and smaller scale maps for free. Earlier, these were restricted for national security reasons. This is a major step forward for open geospatial data in India.
How to Download SOI Maps¶
Method 1: SOI Geoportal (Recommended) 🟡¶
- Go to https://onlinemaps.surveyofindia.gov.in
- Register with your email and mobile number
- Login and navigate to "Free Open Series Maps"
- Select the toposheet index number for your area of interest
- Download the raster (GeoTIFF) or vector (Shapefile) version
How to find your toposheet number: - Use the Index Map on the portal to click your area - The 1:50,000 series uses codes like "55D/10" (Sheet 55D, Division 10)
Method 2: SRTM DEM (Elevation Data) 🟢¶
For elevation data, the SRTM (Shuttle Radar Topography Mission) data from NASA/USGS is free and covers all of India at 30m resolution:
- Go to https://earthexplorer.usgs.gov (free registration)
- Draw your area of interest on the map
- Under "Data Sets" → Select "SRTM 1 Arc-Second Global"
- Click Results → Download the GeoTIFF tile
Alternative — SRTM via Python (no browser needed):
# Using elevation library to get SRTM data
pip install elevation
import elevation
import subprocess
# Download DEM for a bounding box (e.g., Maharashtra)
# west, south, east, north
elevation.clip(bounds=(72.6, 15.6, 80.9, 22.1), output='maharashtra_dem.tif')
# Cleanup cache
elevation.clean()
Reading Topographic Maps¶
SOI topographic maps use standard symbols. Key features:
| Symbol | Feature |
|---|---|
| Brown lines | Contours (elevation) |
| Blue lines | Rivers, streams, canals |
| Black dots | Settlements |
| Red lines | Roads and tracks |
| Green areas | Forests |
| Yellow areas | Agricultural / cultivated land |
Limitations¶
Restrictions on Large-Scale Data
Maps at scale 1:25,000 and larger (more detailed) are still restricted and require formal application to SOI. This includes detailed city maps used for cadastral/property surveys.
✏️ Practice Exercise¶
Exercise 1.6 — Download and Visualise a Toposheet
Goal: Download an SOI 1:50,000 toposheet for your area.
- Register on onlinemaps.surveyofindia.gov.in
- Find the toposheet covering your home area using the index map
- Download the GeoTIFF version
- Open in QGIS — it should automatically georeference to the correct location
- Use the Identify Features tool to click on points and read their coordinates
Bonus: Download the matching SRTM DEM and overlay it with hillshading (QGIS → Raster → Analysis → Hillshade). This creates a beautiful 3D-looking terrain map!
Continue to Chapter 2: Socio-Economic & Demographic Data →