Geographic data can be organized into three basic geometry types: points, lines, and polygons. The creation of these representations must follow appropriate criteria and procedures to ensure accuracy, consistency, and usability.
Common Problems in Geographic Representations
Figure 1 illustrates three classic problems commonly found in the construction of geographic features. In examples (a) and (b), line intersections occur due to errors in the construction of the line and polygon geometries, respectively.
In example (c), a line contains an unnecessary vertex between its two endpoints, even though the feature is a straight line. Vertices should only be used where the direction of a line changes, creating an angle between segments. Unnecessary vertices increase file sizes (such as Shapefile and KML files) and require additional storage space in databases.
Figure 1 – Common Problems in Geographic Representations
Building Line Features
Line geometries also require special attention (Figure 2).
In example (a), the lines are not properly connected. The vertices of the three segments should coincide, as shown in (b). This issue is very common when creating geographic representations of roads, highways, and other transportation networks.
Figure 2 – Construction of Line Features
Building Polygon Features
When two distinct polygons share a boundary or interface, their vertices must coincide precisely along the shared border.
This situation commonly occurs when representing municipal boundaries and other administrative divisions.
In Figure 3, the two polygons shown in (a) are not correctly connected. In representation (b), the shared boundary is properly constructed because the vertices coincide, creating an accurate interface between the two polygons.
Figure 3 – Construction of Polygon Features
Importance of Proper Geometry Construction
The concepts presented in this article are fundamental for ensuring that geographic analyses can be performed correctly and that high-quality maps can be produced.
Accurate construction of points, lines, and polygons contributes to:
- Reliable spatial analysis.
- Correct topological relationships.
- Improved map quality.
- Better interoperability between GIS systems.
- More efficient data storage and processing.
- Reduced errors in geographic databases.
Most GIS and mapping software applications provide specific editing tools designed to assist users in connecting vertices correctly and maintaining topological consistency between lines and polygons.
Proper geometry construction is one of the key foundations of geospatial data quality and should be considered throughout the entire data creation and maintenance process.