Vector Data

A more complex, but light weight format best suited for discrete objects.

Vector Data Model

Represents objects as sets of coordinate pairs.

  • Linked to descriptive attributes.
  • Many attributes per object.

Points

A point feature is an individual x, y coordinate pair representing a precise location.

  • “Zero-dimensional”
  • No length, width, or area

Points

Points are great for representing a variety of objects, depending on the scale:

  • Trees
  • Stop signs
  • Fire hydrants

Points

Points are great for representing a variety of objects, depending on the scale:

  • Trees
  • Stop signs
  • Fire hydrants
  • Cities
  • Wild fires
  • Airports

Lines

A line feature is a set of connected points. Must have a start and end point. May have middle points (vertices).

  • One-dimensional
  • Length
  • No width or area

Lines

Lines are also great, depending on the scale:

  • Hiking trails
  • Power lines
  • Water pipes

Lines

Lines are also great, depending on the scale:

  • Hiking trails
  • Power lines
  • Water pipes
  • Roads
  • Rivers
  • Storm tracks

Polygons

A polygon feature consist of a set of three or more vertices connected by line segments (edges) that form an enclosed shape.

  • One-dimensional
  • Length & width
  • Area

Polygons

Preferred for many objects depending on scale:

  • Climate units
  • Lakes
  • Political boundaries

Polygons

Preferred for many objects depending on scale:

  • Climate units
  • Lakes
  • Political boundaries
  • Buildings
  • Roads
  • Cities

interior rings

All polygons are an enclosed shape. Some can also have interior rings (holes).

  • Each ring is a separate set of vertices and edges within the polygon.
  • Interior rings cannot overlap.

Multi-part Vectors

When an object has multiple parts, the vector model allows for:

  • Multi-polygons
  • Multi-lines
  • Multi-points

Resolution

Data resolution also applies to the vector model:

  • Less straightforward than for raster model
  • Space between vertices
  • Higher resolution = larger filed size

Tabular Data

Non-spatial data can be stored in an Attribute Tabule separate from the spatial data.

Tabular Data

Tabular Data

Ability to store many attributes:

  • Less redundancy than raster model
  • Easy to add new attributes

Key Advantages

  • Compact data structure
    • Smaller file sizes
  • Good for discrete objects
    • Graphic output is usually "cleaner"
  • Easy to query and select by attributes
  • Topology (connectivity) - Proximity & Network Analysis

Main Disadvantages

  • Complex data structures compared to rasters
  • Topology (connectivity) - can be a huge head ache when creating a layer
  • Some tasks (overlay of layers) can be computationally expensive
  • No variability within polygons possible.
  • Less suited for continuous variables (requires significant generalization)

Shapefiles (.shp)

One of the most common file types you will encounter, stores the coordinates of vertices plus metadata:

  • Object type: points/multi-points, lines/multi-lines, or polygons/multi-polygons.
    • Only one type per .shp!
  • Coordinate reference system (CRS).
  • Attribute table.

GeoJson (.json)

A simple, lightweight format for most commonly encountered in web mapping.

  • Unlike shapefiles, a GeoJSON can mix of geometries.
  • Encoded stylistic choices in the file.
  • Larger File Size
  • An Example