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Spatial Data Formats

Spatial Data Formats. Stages of development:. Conceptual model : select the features of reality to be modeled and decide what entities will represent them Spatial data model : select a format that will represent the model entities

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Spatial Data Formats

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  1. Spatial Data Formats CS 128/ES 228 - Lecture 4b

  2. Stages of development: • Conceptual model: select the features of reality to be modeled and decide what entities will represent them • Spatial data model: select a format that will represent the model entities • 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 • Raster • Vector • 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 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: Equilateral triangle Square 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. 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 Advantages of raster format CS 128/ES 228 - Lecture 4b

  16. 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 Limitations of raster format 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 CS 128/ES 228 - Lecture 4b

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