Tool for Locating Constructable Terrain to Facilitate Development Planning
Scott Sexton, a resourceful individual with a knack for problem-solving, found himself in a predicament common to many builders – the search for usable, non-steep land for future construction projects. With the help of Geographic Information Systems (GIS), he managed to devise a method to extract steepness and grade information from topographical maps, overcoming the limitations of existing resources.
In his quest, Sexton encountered examples of what can go wrong when digital mapping data is used without proper sanity checks. He knew from past experience that a high concentration of topographical lines on maps indicated steeper areas. However, he was unsure about how to get a computer to parse topographical maps and provide information on steepness and grade.
To tackle this challenge, Sexton turned to GIS. He downloaded USGS elevation data in three-meter resolution, considering USGS maps as a potential source of information, but they lacked grade information. Undeterred, he tweaked the output of his tools and automated the process, generating usability maps of areas of interest.
The key to his method lies in the integration of USGS Digital Elevation Models (DEMs) with GIS slope calculations and the calculus concept of gradients. By doing so, he effectively found and mapped flatter zones ideal for construction projects.
Here's a step-by-step guide on how to follow in Sexton's footsteps:
1. Obtain USGS Elevation Data (DEMs) - Download DEMs from USGS EarthExplorer, which offers access to high-resolution elevation datasets such as ASTER DEMs and others suitable for detailed terrain analysis. - Alternatively, use dynamic elevation layers available through platforms like ArcGIS Online that provide multi-resolution global elevation data for visualization and analysis.
2. Load Data into GIS Software - Import the downloaded DEM into GIS software like ArcGIS, QGIS, or similar. - Ensure the DEM is properly georeferenced to align with your area of interest.
3. Calculate Slope Using GIS Tools - Use GIS spatial analyst functions to compute slope, which is the rate of change of elevation over horizontal distance. - The slope output layer will express steepness as degrees or percent. - Flatter areas for building are typically identified by low slope values (near 0° or 0% slope).
4. Mathematical and Calculus-Based Analysis of Terrain - The slope at any point on a continuous surface is the magnitude of the gradient vector of the elevation function \( z = f(x,y) \): \[ \text{slope} = \sqrt{\left(\frac{\partial z}{\partial x}\right)^2 + \left(\frac{\partial z}{\partial y}\right)^2} \] - GIS software approximates these partial derivatives from the DEM grid cells using finite difference methods. - You can analyze the gradient (slope) numerically or visualize it to pinpoint areas with minimal slope magnitude, indicating flatter terrain.
5. Further Terrain Analysis (Optional) - Calculate aspect (direction the slope faces) if sun exposure or wind is also a factor. - Use curvature analysis for understanding concavity/convexity of the terrain which affects drainage and stability. - Use these parameters to refine site suitability for construction.
6. Identify Suitable Building Areas - Apply threshold criteria to the slope layer (e.g., slope < 5°) to extract polygons/regions considered flat enough. - Combine with other spatial data (land cover, roads, soil) for comprehensive site selection.
By integrating USGS DEMs with GIS slope calculations and the calculus concept of gradients, you can effectively find and map flatter zones ideal for construction projects. If you wish, I can guide you through specific GIS steps or provide example scripts for slope calculation.
Scott Sexton's usability project may be of interest to those who tinker with GIS work. If readers have their own GIS hacks, they can notify via the tipsline.
- Intrigued by the challenge of finding suitable construction sites, Scott Sexton utilized science, technology, and data-and-cloud-computing to devise a method involving USGS Digital Elevation Models (DEMs) and GIS slope calculations.
- Employing calculus concepts such as gradients, Sexton developed a system to automatically identify flatter zones on topographical maps for potential construction projects, demonstrating the power of combining technology with GIS and USGS DEMs.
