• Spatial data refers to geographic areas or features. Features occupy location.
• Non-spatial data has no specific location in space. It can however, have a geographic component and be linked to a geographic location
• Tabular and attribute data are non-spatial but can be linked to location.
• Example: In the Portland map, a park is a spatial feature and the associated information about the park name, area, administrative code and type code are non-spatial attributes which are linked to the park by its location.
  

Themes

• Themes link features by geography and with their attributes
• Collections of themes form a GIS database
  
  

Take, for example, the Portland map. It contains many themes. All the interstate freeways could make up one theme, and all railroads, another. City streets might be a separate theme. Parks, buildings, and waterways are examples of other themes.

Geographic databases (themes) can be used to solve problems like:

• Site Location
  visualizing customer locations is critical to businesses trying to make better marketing decisions.

Analyzing location is a key to making decisions about where to set up a business or service.

Presenting information as maps reveals relationships and patterns that may otherwise be hidden.

• Other applications include:
  • tracking delivery vehicles
  • recording details of planning applications
  • modeling global atmospheric circulation

Geo-coding and Geo-referencing
How to encode locational information?

How do we reference locations?

Explicit Geographic Reference

• latitude and longitude
• national grid coordinate

Implicit Geographic Reference

• postal code
• census tract name
• forest stand identifier
• road name

Geocoding
Geocoding = deriving implicit from explicit references
these geographic references allow you to locate features (like a business or forest stand) and events (like an earthquake) on the surface of the earth for analysis.

Example of Geocoding:

Data Models
There are two fundamentally different types of geographic information.

The vector model

• Information about points, lines, and polygons
• Encoded and stored as a collection of x, y coordinates
  The location of a point feature, such as a bore hole, can be described by a single x, y coordinate. Linear features, such as roads and rivers, can be stored as a collection of point coordinates. Polygonal features, such as sales territories and river catchments, can be stored as a closed loop of coordinates. The vector model is extremely useful for describing discrete features, but less useful for describing continuously varying features such as soil type or accessibility costs for hospitals.
  

The raster model

• Models are continuous features
• A collection of grid cells
  Both the vector and raster models for storing geographic data have unique advantages and disadvantages. Modern GIS is able to handle both types of models.

Overview | Other Defination |Components of GIS|How GIS work

Task of GIS|Queries a GIS can answer|