As discussed in the article Data Quality, the creation of geographic representations of points, lines, and polygons must follow appropriate criteria and procedures.
In this article, we address additional important aspects of spatial data organization, using sugarcane field plots as an example (Figure 1).
Figure 1 – Representation of sugarcane field plots
The recommendations below are primarily intended for CAD software users who export DWG or DXF maps to formats commonly used in GIS software, such as Shapefile and KML.
1. Content
Draft Elements
It is important that CAD files do not contain draft elements, sketches, or temporary drawings when they are exported or converted to other formats (Shapefile, KML, etc.).
Figures 2 and 3 show examples of CAD files containing draft features that were imported into GIS software.
In Figure 2, the polygons on the left correctly represent a farm. The polygons on the right should not be part of the CAD file and represent draft elements that must be removed.
Figure 2 – Farm draft features (right side)
In the example shown in Figure 3, it is impossible to determine whether the upper or lower farm boundary is the correct representation.
Figure 3 – Farm draft features
2. Georeferencing
Misaligned Features
Satellite imagery can easily be used to verify whether a farm has been georeferenced correctly.
The example in Figure 4 shows a farm polygon that was incorrectly created and is located in the wrong position.
Figure 4 – Misaligned farm polygon
Distorted Geometry
In some cases, a lack of proportionality becomes evident when part of the farm is correctly georeferenced while another part is not.
The red arrows in Figure 5 indicate the portion of the farm that is out of position.
Figure 5 – Farm with distorted georeferencing
3. Geometry Issues
Lines with Excessive Vertices
Geographic representations of lines and polygons should contain the minimum number of nodes or vertices necessary to accurately represent the feature.
This is important because it improves:
- Spatial analysis performance
- Geometry editing and maintenance
- Database storage efficiency
Figure 6 illustrates a field polygon containing an excessive number of vertices.
Figure 6 – Polygon vertices
Duplicate Vertices
During the creation of line and polygon geometries, accidental double-clicks may create duplicate vertices at the same location.
The duplicated point shown in Figure 7 must be identified and removed to prevent errors during future GIS operations.
Figure 7 – Duplicate vertices
Polygon Overlap
Overlap between field plots (polygons) frequently occurs when farms created in different CAD files are merged into a single dataset.
In Figure 8, the overlap highlighted by the red arrow occurred because the polygon on the left, originating from a different CAD file, was not positioned correctly.
Figure 8 – Polygon overlap
Polygon Holes (Interior Rings)
Field plots often contain islands formed by vegetation, ponds, quarries, or other excluded areas. These features should be represented using polygon holes (interior rings).
In Figure 9, the upper image illustrates an incorrect representation, while the lower image demonstrates the proper use of an interior ring.
Figure 9 – Creating polygon holes (interior rings)
Benefits of Proper Geographic Data Organization
Well-organized geographic representations support several important GIS activities, including:
- Geometric operations such as difference, clipping, and intersection.
- Accurate calculations of area, perimeter, distance, and other spatial measurements.
- Reduction of geometry file size (SHP, KML, etc.), improving the performance of GIS software and web-based applications.
Proper spatial data organization is essential for ensuring data quality, improving analytical accuracy, and increasing the efficiency of geospatial systems and workflows.
For additional information about organizing geographic data, see the article Data Quality.