7 - Spatial data structures Flashcards
4 levels of abstraction
- Real world
- Data model
- Data structure
- File structure
Spatial data model
Simplified representation of spatial
features or spatial phenomena on the Earth’s surface
Topology refers to
The spatial relationships that exists between features in a feature layer in the vector model
Topology is the
- Connection between lines,
- Shared boundaries between areas
- Inclusion of points in areas
Digital models used to store vector objects
- Georelational Model
- Object Based Data Model
Georelational Data Model includes
Geometry (spatial features)
Attributes (relational data)
File formats in which maps are created from ARCGIS
Arpx & MXD
Arpx & MXD store..?
- maps
- symbology,
- layout
- hyperlinks
- toolbars added,
files required to make a shapefile
- .shp,
- .shx
- .dbf.
Advantages of the georelational shapefile
- Display faster
- Non-proprietary & interoperable
Disadvantages of georelational shapefile
- Shapes can overlay
- Boundaries must be stored twice
- Very little error checking
- Data quality issues
A coverage def
Georelational data model that stores vector data - contains both the spatial (location) and attribute (descriptive) data for geographic features.
When was the coverage introduced?
ArcInfo in early 80s
How many files in the coverage?
12
OODM
Object Orientated Data Model
- treats geospatial data as objects
Property def
Describe an attribute of features in layer
Method def
Performs an action to layer
Feature class def
Store spatial features of same geometry
Feature dataset
Store features that share extent and coordinate system
How is OODM different from Georelational Model?
- Feature geometry (stored in special field = BLOB) & attributes are stored in one system.
- allows spatial features to be associated with a set of properties and methods
BLOB
Binary large object data type
Feature class
Store spatial features of same geometry
Feature dataset
Store features that share extent and coordinate system
