Vector Geometry Types
Geographic Information Systems (GIS) use vector geometry to represent real-world features on a map. Understanding these vector geometry types is essential for anyone working with GIS data. This guide covers the basics of vector geometry types, including advanced types.
What is Vector Geometry in GIS?
Vector geometry represents spatial data using points, lines, polygons, and their advanced forms. Each geometry type serves a unique purpose in mapping and spatial analysis.
Primary Vector Geometry Types
Point
A point is a single coordinate representing a specific location in space. It's defined by its X (longitude) and Y (latitude) coordinates.
Points are used to represent discrete locations, such as:
- Landmarks
- Addresses
- Trees
- Sampling locations
Example: A point representing the location of a fire hydrant would have coordinates (X, Y).
Line
A line (or polyline) is a series of connected points forming a path. It’s defined by multiple coordinate pairs.
Lines represent linear features, such as:
- Roads and highways
- Rivers and streams
- Hiking trails
- Utility lines
Example: A line representing a river might start at one coordinate pair and end at another, connecting several intermediate points.
Polygon
A polygon is a closed shape formed by multiple connected lines. The first and last points are the same, creating an enclosed area.
Polygons are used to represent areas, such as:
- Parcels of land
- Lakes and ponds
- Buildings
- City boundaries
Example: A polygon representing a park would have multiple coordinates outlining its perimeter.
Advanced Vector Geometry Types
MultiPoint
A multipoint is a collection of points grouped into a single geometry.
Multipoints are useful for representing multiple locations that are part of a single entity, such as:
- Clusters of trees
- Grouped survey markers
Example: A multipoint geometry could represent a group of the same species of tree locations within a study area.
MultiLine
A multiline (or multilinestring) is a collection of lines grouped into a single geometry.
Multilines are used for representing multiple linear features that are related, such as:
- Network of paths within a park
- Sections of a disjointed road
Example: A multiline geometry could represent different trails within a hiking area.
MultiPolygon
A multipolygon is a collection of polygons grouped into a single geometry.
Multipolygons are ideal for representing multiple area features that belong together, such as:
- Islands of an archipelago
- Different parcels of land owned by one entity
Example: A multipolygon geometry could represent various protected areas within a national park.
Geometry Collections
A geometry collection is a complex type that groups different geometries (points, lines, and polygons) into a single entity.
Geometry collections are used when a single feature needs to be represented by multiple types of geometries, such as:
- A city map with landmarks (points), roads (lines), and districts (polygons)
- A construction site with different types of spatial data
Example: A geometry collection could include the location of buildings (polygons), paths (lines), and trees (points) within a university campus.
Key Takeaways
- Points: Represent single locations with X, Y coordinates.
- Lines: Represent paths or connections between multiple points.
- Polygons: Represent areas enclosed by connected lines.
- Multipoints: Group multiple points into a single geometry.
- Multilines: Group multiple lines into a single geometry.
- Multipolygons: Group multiple polygons into a single geometry.
- Geometry Collections: Combine different geometry types into a single entity
By understanding these vector geometry types, including their advanced forms, you can better manage and analyze your GIS data, leading to more accurate and meaningful insights.