Surveying techniques in Geographic Information Systems (GIS) involve the methods and tools used to accurately determine the spatial location of features on the Earth’s surface. These techniques are foundational for building accurate GIS databases. Here’s a breakdown of the key surveying techniques used in GIS:
1. Traditional Surveying (Total Station, Theodolite, Leveling)
- Instruments: Total stations, theodolites, auto-levels
- Process: Measures angles and distances from known points to determine coordinates of unknown points.
- Accuracy: Very high; often used for engineering and cadastral surveys.
- Use in GIS: Provides precise control points and basemaps for GIS layers.
2. Global Navigation Satellite Systems (GNSS/GPS)
- Types:
- Handheld GPS: For general location mapping (lower accuracy).
- Differential GPS (DGPS): Enhanced accuracy by correcting GPS signal errors.
- Real-Time Kinematic (RTK) GPS: High-precision (centimeter-level), real-time corrections.
- Use in GIS: Widely used for data collection in environmental mapping, urban planning, utilities, and infrastructure.
3. Remote Sensing
- Tools: Satellites (e.g., Landsat, Sentinel), UAVs/drones, aerial photography.
- Output: Raster data (images), which can be georeferenced and analyzed in GIS.
- Use in GIS: Land use/land cover classification, change detection, vegetation analysis.
4. Photogrammetry
- Process: Uses stereo images (typically from aircraft or drones) to derive 3D coordinates.
- Use in GIS: Used for topographic mapping, DEM generation, and urban modeling.
5. LiDAR (Light Detection and Ranging)
- Process: Uses laser pulses to measure distances and generate high-resolution 3D point clouds.
- Platforms: Airborne (drones, aircraft) or terrestrial.
- Use in GIS: Highly accurate terrain models, forestry analysis, flood modeling, and infrastructure planning.
6. Mobile Mapping Systems
- Instruments: Vehicle-mounted GPS, LiDAR, cameras.
- Use: Rapid data collection along roads and urban environments.
- Use in GIS: Road networks, street furniture, utility mapping.
7. Cadastral Surveying
- Purpose: Defines legal property boundaries.
- Tools: Often combines total stations and GNSS.
- Use in GIS: Land ownership and parcel mapping.
8. Hydrographic Surveying
- Purpose: Surveys underwater terrain (bathymetry).
- Tools: Sonar, GPS, echo sounders.
- Use in GIS: Coastal zone management, flood risk modeling, waterway mapping.
Summary Table
| Technique | Accuracy | Common Use Case in GIS |
|---|---|---|
| Total Station | High (mm-cm) | Cadastral, engineering basemaps |
| GPS/GNSS | Medium to high | Field mapping, asset location |
| Remote Sensing | Medium | Land use, environmental monitoring |
| Photogrammetry | High | Topographic mapping, 3D modeling |
| LiDAR | Very high | DEMs, vegetation, urban modeling |
| Mobile Mapping | High | Road assets, urban infrastructure |
| Cadastral Surveying | Very high | Legal land boundaries |
| Hydrographic Surveying | Medium to high | Underwater terrain, coastal management |
