Lecture Notes for Clarke, K. C. Analytical and Computer Cartography

"The Spatial Data Transfer Standard has provided cartographers with a consistent set of terminology and concepts, known as a data model, around which data structures can be developed." (Clarke, p. 115)

- Data Model maps onto a data structure
- Data structure eventually implies programming structure
- Unstructured computer programming languages did not support data structures well
- Structured languages (e.g. C, Pascal) allow definition of structures directly
- Link between the physical storage of data and the data's use in mapping systems

- Draft standard published in The American Cartographer (1988)
- FIPS 173 approved 1992
- Standard consists of several sections
- Introduction
- Spatial Data Concepts
- Formalization of spatial data and models
- Entity Instance: A spatial phenomenon of a defined type
- Entity Object: A digital representation of an entity instance.

- Spatial Data Quality
- Lineage
- Positional Accuracy
- Attribute Accuracy
- Logical Consistency
- Completeness

- General Specification
- Uses Modules
- Transfer takes place in ISO 8211 formats
- Large number of feature types and language descriptions at 2 levels

- Most primitive object is the POINT
- Can be (x,y) or (x,y,z)
- Consists of geocodes for location in a standard system
- Should be in world not image geometry
- If significant topologically, is a node.
- Can identify a feature (entity) or a label (label)
- Can be INSIDE an area and carry its identification information

- Divide up by lines with and without topological significance
- Primitive object is the segment
- Segments connect to make a string (line or polyline)
- If defined mathematically, use arc
- If line segment connects nodes, called a link (for a network)
- Topological versions carry end node and or left and right polygon data
- Complete, area and network chain versions
- Area-like objects are G-ring and GT-ring

- Interior area is the space contained by the polygon, i.e. the object not the boundary
- G-polygon contains graphical objects that form a polygon, e.g. a ring
- GT-polygon contains conplete topology
- Toplogical encoding requires
**universe**and**void**polygons. - Special objects
- pixel (the smallest non-divisible element of a digital image)
- Grid cell (same as pixel but for a grid)

two dimensional array of regular pixels

Set of grid cells forming a regular or near regular tesselation

- Areally distributed set of spatial data representing entity instances within on theme, or with a common attribute.
- Usually registered with other layers.

One or more overlapping layers from the same grid or digital image.

RED

GREEN

BLUE

**Planar Graph**: Node and link/chain set as applied to a plane surface

**Two-dimensional Manifold**: Planar graph with all included objects

**Network: **A graph without two-dimensional objects (links do not have to intersect)

- Three dimensional objects
- time-sensitive objects
- Links to other standards e.g. PHIGS, GKS
- Implementation slow via profiles

Keith C. Clarke Last Update 4/21/97 Copyright Prentice Hall (1995)