CS 128/ES 228 - Lecture 4b1 Spatial Data Formats.
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Transcript of CS 128/ES 228 - Lecture 4b1 Spatial Data Formats.
CS 128/ES 228 - Lecture 4b 1
Spatial Data Formats
CS 128/ES 228 - Lecture 4b 2
Stages of development:
1. Conceptual model: select the features of reality to be modeled and decide what entities will represent them
2. Spatial data model: select a format that will represent the model entities
3. Spatial data structure: decide how to code the entities in the model’s data files
CS 128/ES 228 - Lecture 4b 3
2. Spatial data models
1. Raster
2. Vector
3. Object-oriented
Spatial data formats:
CS 128/ES 228 - Lecture 4b 4
Raster format
Features represented by cell contents
Spatial precision limited by cell size
Surfaces modeled as continuous values (almost)
CS 128/ES 228 - Lecture 4b 5
Vector format Discrete features
explicitly represented
Spatial precision limited by number format
Surfaces shown by contours rather than continuous values
CS 128/ES 228 - Lecture 4b 6
Object-oriented formats
Leave details for CS majors
CS 128/ES 228 - Lecture 4b 7
Thematic data (a.k.a. “attribute data”)
Quantitative or descriptive
May represent 1 or many themes
Tied to a spatial reference
Represented differently in raster vs. vector formats
CS 128/ES 228 - Lecture 4b 8
Scales of measurement
Data Unit Scale
Resort name text Nominal
Resort ranking value Ordinal
Winter temp. oC Interval
Size of ski area m2 Ratio
Heywood et. al. 2002 – Table 2.1
CS 128/ES 228 - Lecture 4b 9
Spatial modeling in raster format
Basic entity is the cell
Region represented by a tiling of cells
Cell size = resolution
Attribute data linked to individual cells
CS 128/ES 228 - Lecture 4b 10
Tesselation
A closed shape or polygon that repeats on all sides without any gaps or overlaps
Three regular polygons tesselate the plane:
Square Equilateral triangle Hexagon
CS 128/ES 228 - Lecture 4b 11
Tilings
In 1922 Escher visited the Alhambra palace and saw the wall tilings of the Moors. He was excited to find other artists who had been captivated by tilings, but also made this revealing comment: "What a pity their religion forbade them to make graven images."
CS 128/ES 228 - Lecture 4b 12
Escher’s “tesselations”
CS 128/ES 228 - Lecture 4b 13
Quilters also tesselate
Designing Tesselations by Jinny Beyer
CS 128/ES 228 - Lecture 4b 14
Effects of resolution – raster
Larger cells: less precise
spatial fix
line + boundary thickening
features too close overlap - less detail possible
CS 128/ES 228 - Lecture 4b 15
Advantages of raster format
many data sets available
easy to overlay multiple themes
able to represent multiple continuous surfaces
different file formats readily inter-converted
fast computer lookup and display
CS 128/ES 228 - Lecture 4b 16
Limitations of raster format
poor representation of discrete objects
constant resolution throughout region modeled
exact boundary location difficult
difficult to change projection or coordinate system
generates very large data sets
CS 128/ES 228 - Lecture 4b 17
Summary: Raster format
A huge amount of spatial data are available in raster format
Rasters are the format of choice for continuous features
Rasters do a poor job of representing discrete features