Comparing heights relative to a reference point or surface is a common task in geographic analysis. Whether you are assessing the height of buildings above the surrounding terrain or analyzing topographic variations relative to specific features, ArcGIS provides powerful tools to facilitate height compare effectively. This article will guide you through using ArcGIS to calculate and visualize height differences, focusing on the Euclidean Allocation and Distance Allocation tools.
ArcGIS offers robust solutions for spatial analysis, and when it comes to height compare, two tools stand out: Euclidean Allocation and Distance Allocation. These tools are instrumental in creating buffer regions around source points and subsequently enabling the calculation of height offsets relative to these sources. By leveraging these functionalities, users can gain valuable insights into elevation variations within their spatial data.
Let’s delve into how these tools can be applied for height compare.
Euclidean Allocation for Height Buffering
The Euclidean Allocation tool in ArcGIS is a fundamental function for creating allocation rasters. For height compare, we can utilize this tool to generate buffer regions around source points, with the buffer radius potentially defined by a maximum distance parameter. To incorporate height information, an integer field representing the rounded heights of the source features should be added. By specifying this height field as the source_field in the Euclidean Allocation tool, the tool not only buffers but also allocates cells based on proximity to the sources, considering their height attributes.
This process is crucial for height compare as it establishes zones of influence around each source point, weighted by their respective heights. The result is an allocation raster where each cell is assigned to the nearest source, effectively creating height-based buffer zones.
Distance Allocation: Considering Surface Distance
While Euclidean Allocation calculates distance in a planar, straight-line manner, the Distance Allocation tool offers a significant enhancement for height compare by calculating true surface distance. This is particularly relevant in terrain analysis where the actual distance along the surface can differ substantially from the planar distance. For applications requiring accurate height compare in complex terrains, Distance Allocation becomes invaluable.
Similar to Euclidean Allocation, Distance Allocation can utilize a maximum accumulation parameter to define buffer radii and a source_field to incorporate height values. The key advantage here is the ability to measure distance over the elevation surface, providing a more realistic representation of spatial relationships for height compare.
The image above illustrates the difference between planar Euclidean distance (blue circle) and true surface distance (red-white-green buffer). For accurate height compare in hilly or mountainous regions, surface distance provides a more precise buffer, reflecting real-world measurements.
Visualizing Relative Heights
Once the allocation raster is generated using either Euclidean or Distance Allocation with height as a source attribute, the next step in height compare is to calculate and visualize the height offsets. This is achieved by subtracting the allocation raster from the original elevation surface. The resulting raster will represent the height difference relative to the source points. Areas outside the buffer zones will naturally be represented as NODATA, effectively isolating the areas of interest for height compare.
Visualization of these relative heights can be enhanced through reclassification or by using a stretch renderer. A multi-part stretch renderer, with the midpoint set to zero, is particularly effective for highlighting areas above and below the source heights. For instance, shades of green can represent areas above the source elevation, red for areas below, and white for areas at approximately the same elevation. This visual representation greatly aids in understanding and communicating the height compare results.
Advanced Height Comparison Techniques
For more advanced height compare analyses, consider the Zonal Statistics as Table tool. While the initial methods focus on comparing heights relative to individual sources, Zonal Statistics can be employed to compare heights relative to the average height within buffer regions. This is particularly useful when you need to assess how elevations deviate from the mean elevation within defined zones.
To implement this for height compare, you would first use the Buffer GP tool to create overlapping buffer zones around your source points. Then, utilize Zonal Statistics as Table to calculate the mean elevation within each buffer zone (handling overlaps). Assign these mean values back to the source points and proceed with the allocation and subtraction steps as described earlier. This approach, while not utilizing surface distance buffers, provides a valuable alternative for height compare based on average zonal heights.
In conclusion, ArcGIS offers a powerful suite of tools for conducting height compare analyses. By strategically employing Euclidean Allocation and Distance Allocation, coupled with effective visualization techniques, users can gain profound insights into relative elevation differences within their spatial data, catering to a wide range of applications from urban planning to environmental analysis.
