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Upland and Lake areas do not overlap. There are no gaps between the Upland and Lake areas.The aquatic vegetation polygons do not overlap.The aquatic vegetation layer is contained within the lakes layer.All layers are contained within the study area defined by the SouthBayArea polyline.
Advanced Editing and Topology
Introduction
Last week, we were introduced to the art of digitization, how to use it, and its importance in the GIS and UAS industry. This week, we furthered our skills by creating, validating, and editing topology. Topology is a set of rules that define how points, lines, and polygons relate to one another. It prevents errors such as overlaps and gaps, enabling accurate analysis. In this lab, we were provided with data from a set of lakes in Minnesota. We were tasked with digitizing the boundary to depict the difference between the lakes, the upland, and the aquatic vegetation. Then, we were to create a set of rules that our geometry would need to follow.
Resources Used
Steps/Process
To practice using geographic software systems to implement topologies, we were provided with a practice map of a small area in southern France. This map was a geodatabase that provided digitization of the buildings, roads, and landcover in the area. The purpose of the topology for this section is to restrict certain layers, eliminate gaps and slivers, and to reduce overlap between certain layers. We implemented the following rules, shown in Figure 1.
Figure 1. Besset Topology Rules
In addition to these rules, we also changed the XY cluster tolerance to 0.5 meters. The XY cluster tolerance defines the horizontal distance threshold within which vertices are shared and snapped together during validation. The following map was created before validating the topology.
After running the topology, errors are identified in pink and green, showing the expectations. After practicing the topology on the Besset map, it was time to create and run our own topology.
Our assignment was to create a topologically correct map with three layers: Uplands, Lakes, and Aquatic Vegetation in the Big Marine Lake in Washington County. The first step in creating this map was to create a dataset with three feature classes in the UTM North America zone 15N NAD83 (2011). The next step was to digitize each layer boundary. To guide us, we had a boundary of where we were supposed to digitize and a summer and spring image of the lake to help identify each boundary. To help speed up the process, we learned new skills like merging, clipping, tracing existing edges, and crosshatch fills.
Once the digitization was completed, it was time to write our topology rules. In order to do this correctly, we needed to turn our boundary line layer into a polygon. This was to ensure our topology was contained in the specific boundary. Below are the topological rules added and the final map.
Summary
This lab introduced the concept of topology and emphasized its critical role within the GIS industry. Topology supports data integrity by ensuring accurate validation and consistent spatial relationships. When applied to the UAS industry, topology enables advanced capabilities such as autonomous flight, 3D modeling, risk analysis, traffic management, and improved operational safety. Developing a strong understanding of topology will be highly beneficial to my future career.
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