Polygon digitization in ArcGIS Pro follows a process similar to that of polylines. It is advisable to disable all unnecessary vector layers in the “Contents” panel to minimize confusion and ensure precision during the digitizing process.
To initiate polygon creation, the target layer—such as “plant_cover”—must be selected from the “Create Features > Templates” panel. Then, click on the “Polygon, Create a polygon feature” button to begin drawing. The process starts by marking the first vertex and then outlining the boundary of the area. The shape is completed by double-clicking the final point or pressing the “F2” key. Various polygon categories can be assigned, such as grassland, crops, or forest, depending on the specific classification requirements.
To maintain topological accuracy, specific considerations must be observed to avoid issues that may require later corrections.
Polygon editing in ArcGIS Pro
It is essential to avoid topological errors, including gaps, voids, and overlaps between adjacent polygons. These errors can be difficult to detect visually and are often only noticeable upon zooming in and examining the polygon boundaries in detail. Shared areas between polygons are another common issue that can affect the integrity of the spatial data.
Such problems often result from inconsistent editing practices or the integration of data from different sources or scales. Careful attention during digitization and editing is necessary to uphold the accuracy and quality of spatial information.
Maintaining proper topological structure ensures more reliable geospatial analysis and supports efficient data management.
Gaps and overlap in polygons
ArcGIS Pro provides several essential tools for accurate polygon editing. In the “Edit > Tools” tab, tools such as “Split” and “Reshape” are available. Additionally, the “Autocomplete Polygon” option in the “Create Features > Templates” panel plays a key role in maintaining spatial continuity and reducing manual errors. These tools help prevent topological issues and improve the efficiency of the digitization process.
To digitize subdivided areas, it is advisable to first draw the outer boundary and then create the internal divisions. For example, when preparing a land use map, the complete perimeter of the study area should be drawn before segmenting it into specific land cover categories.
Cutting polygons with “Split” tool
To use the “Split” tool, select the polygon via “Edit > Selection > Select”. Once selected, the polygon edges will appear in light blue. Click on the “Split” tool and mark the starting point of the cut outside the polygon. Draw the cutting line through the desired section, ending it again outside the polygon. Confirm the split by double-clicking or pressing “F2”. This process can be repeated to make further internal divisions within the selected polygon. Note that the tool only becomes active when one or more polygons are selected.
Changing the shape to a polygon with “Reshape” tool
To change the geometry of a polygon, select it via “Edit > Selection > Select” and then click the “Reshape” icon under the “Edit > Tools” tab. This function allows for both enlarging and reducing polygon areas.
For enlarging, start and finish the reshaping line inside the polygon. For reducing, the drawing must begin and end outside the polygon. This ensures the reshaped area is added to or subtracted from the polygon correctly, depending on the intended edit.
Autocomplete polygons with “Autocomplete Polygon” tool
When digitizing adjacent polygons, it is important not to duplicate shared boundaries and to ensure continuous alignment. The “Autocomplete Polygon” tool is particularly effective for this purpose. Located in the “Create Features > Templates” panel, this tool allows for seamless creation of new polygons next to existing ones. It is recommended to activate the “Snapping” option to assist in precisely connecting to the edges of neighboring polygons. To use this tool, draw at least two vertices that connect with the edges of adjacent features.
To merge two or more polygons, select them using the “Select” tool while holding the “Shift” key. Then use the “Merge” function located in the “Edit > Tools” tab. During the merge process, a choice must be made regarding which attributes will be retained in the final combined polygon.
For practical application, digitizing elements from a georeferenced image into layers such as “plant_cover” and “lake” is encouraged. Continuous saving is essential to preserve edits and prevent data loss during the session.