(Spatial) Data

What is Data?

[Source]

Spatial Data

• Also known as geospatial data
• Observation that identify the geographic locations of
  • features on the Earth
  • boundaries on the Earth
• Stored as coordinates and topology
• 80-100% of all data have a geographical component (Cressie 1993)

Types of Spatial Data

• Point Pattern Data
• Geostatistical Data
• Lattice (Polygon) Data
• Network Data
• Spatial Interaction Data

Digital Data

In order to encode spatial data, we need a conceptual view that can form the basis for a data model.

By encode, we mean turn data as observations into digital data that can be used in a GISystem

Representation

Two key views of geospatial reality are the:

• object view
• field views

Object View

• the world is viewed as a set of discrete spatial objects (entities)
• can take different forms
  • points: location of a traffic accident
  • lines: stream segment/river segment
  • areas/polygons: Riverside County

Object View

Field View

• geography seen as a collection of continuous variables
• phenomena could be measured everywhere (at any point in space)
• ex: air pollution, elevation, precipitation

Field View

GIS Data Models

GIS Data Models

• Vector Data Model (Today)
• Raster Data Model (Future)

Vector Data Model

• Each discrete object is considered to be a feature
• Vector features have attributes, which consist of text or numerical information that describe the features
• A vector feature has its shape represented using geometry
• The geometry is made up of one or more interconnected vertices

Vector Geometry

• The geometry is made up of one or more interconnected vertices
• A vertex describes a position in space using an X, Y and optionally Z axis.
• Geometries which have vertices with a Z axis are often referred to as 2.5D since they describe height or depth at each vertex, but not both.

Scale and Representation

Scale and Representation

Vector Attributes

Attribute Properties

Issues with Vector Data

• slivers
• under and overshoots
• topological errors

Slivers

Under and overshoots

Next Up

• Vector Tables
• Queries