CS 128/ES Lecture 4b1 Spatial Data Formats

CS 128/ES Lecture 4b2 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 Lecture 4b3 2. Spatial data models 1.Raster 2.Vector 3.Object-oriented Spatial data formats:

CS 128/ES Lecture 4b4 Raster format  Features represented by cell contents  Spatial precision limited by cell size  Surfaces modeled as continuous values (almost)

CS 128/ES Lecture 4b5 Vector format  Discrete features explicitly represented  Spatial precision limited by number format  Surfaces shown by contours rather than continuous values

CS 128/ES Lecture 4b6 Object-oriented formats Leave details for CS majors

CS 128/ES Lecture 4b7 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 Lecture 4b8 Scales of measurement DataUnitScale Resort nametextNominal Resort rankingvalueOrdinal Winter temp. oCoCInterval Size of ski aream2m2 Ratio Heywood et. al – Table 2.1

CS 128/ES Lecture 4b9 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 Lecture 4b10 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 Lecture 4b11 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 Lecture 4b12 Escher’s “tesselations”

CS 128/ES Lecture 4b13 Quilters also tesselate Designing Tesselations by Jinny Beyer

CS 128/ES Lecture 4b14 Effects of resolution – raster Larger cells:  less precise spatial fix  line + boundary thickening  features too close overlap - less detail possible

CS 128/ES Lecture 4b15 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 Lecture 4b16 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 Lecture 4b17 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