Topography Fundamentals: Measuring and Mapping Earth’s Surface
Topography: Defining Earth’s Surface Positions
Topography is the science of determining the relative positions of points on, above, or below the Earth’s surface using distance, elevation, and direction.
Geodesy
Geodesy measures large land areas, considering Earth’s curvature, for mapping, boundary setting, and navigation.
Photogrammetry
Photogrammetry uses photographs to create terrain maps through aerial or terrestrial data collection.
Flat Topography
Flat Topography focuses on small areas, ignoring Earth’s curvature, for land measurement and mapping.
Fundamentals of Flat Topography
This section focuses on flat topography for calculating areas, volumes, distances, and directions.
Planimetry (Horizontal Control)
Planimetry projects the field onto a horizontal plane for measuring distances and areas.
Altimetry (Vertical Control)
Altimetry measures elevation differences between points.
Simultaneous Planimetry and Altimetry
Combining planimetry and altimetry creates topographic maps with contour lines showing elevation.
Surveying Operations
Surveying involves field work and office work.
Field Operations
- Selecting methods, tools, and precision.
- Determining reference points (polygonal base).
- Positioning markers for boundaries and construction.
Height, Elevation, or Cota
Altitude is the vertical distance from mean sea level. Elevation difference between two points is the gap.
Contours
Contour lines on maps represent points of equal elevation, showing terrain relief.
Vertices, Stations, and Stakes
A vertex is where two lines intersect. A station is where a survey instrument is placed. Stakes mark points temporarily or permanently.
- Transit stakes: Short stakes marking instrument locations.
- Chamfer stakes: Stakes marking earthwork points.
- Natural points: Existing features like river banks or rocks.
- Artificial points: Concrete markers with bronze plaques.
Topographic Point References
Distance and angle measurements from a survey point to a stable record define its position.
Leveling Adjustment: Fixing Bounds
- By distance: Error divided by total distance, multiplied by partial distances.
- By instrument positions: Error divided by number of positions, multiplied sequentially.