Data Models - GIS I


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  • Simple routing, one vehicle, multiple stops
  • Service area routing – Maintenance calls are routed to the closest facility
  • Data Models - GIS I

    1. 1. Data Models<br />GIS I<br />
    2. 2. Data Models<br />GIS is an abstraction of reality.<br />A perfect copy of reality cannot be recreated in the computer.<br />We create models – sets of constructs for describing & representing select aspects of the real world in a computer.<br />Models are composed of a mix of raster, vector, and attribute data. <br />Model is tailored to a specific function.<br />
    3. 3. node<br />B<br />node<br />C<br />Polygon<br />I<br />Polygon<br />III<br />node<br />A<br />Polygon<br />II<br />node<br />E<br />node<br />F<br />node<br />D<br />Polygon<br />V<br />Polygon<br />IV<br />node<br />G<br />Coding Vector Data<br />Vector Mode Model of Reality<br />Reality<br />
    4. 4. node<br />B<br />node<br />C<br />Polygon<br />I<br />Polygon<br />III<br />node<br />A<br />Polygon<br />II<br />node<br />E<br />node<br />F<br />node<br />D<br />Polygon<br />V<br />Polygon<br />IV<br />node<br />G<br />
    5. 5. node<br />B<br />node<br />C<br />Polygon<br />I<br />Polygon<br />III<br />node<br />A<br />Polygon<br />II<br />node<br />E<br />node<br />F<br />node<br />D<br />A topologic vector model records the points and linesshared between polygons as unique items, thus every oneof the points and lines are recorded in the data only once.<br />
    6. 6. node<br />B<br />node<br />C<br />node<br />A<br />Polygon<br />II<br />node<br />E<br />node<br />D<br />Polygon 2 is on the right sideof the line ABCED.<br />
    7. 7. Polygon<br />I<br />Polygon<br />III<br />node<br />A<br />Polygon<br />II<br />node<br />E<br />node<br />F<br />node<br />D<br />Polygon<br />V<br />Polygon<br />IV<br />Polygon 2 knows it’s adjacentto Polygons 1, 3, & 4.<br />It shares a line segment with each. <br />Polygon 2 knows it touchesPolygon 5.<br />It shares node E with Polygon 5.<br />
    8. 8. What is Topology?<br />Shared Geometries, Adjacency and Overlap<br />Where points, lines, and polygons share individual vertices. Move a point and it moves a vertex in a line/polygon, and vice versa.<br />Two polygons that share vertices are considered adjacent.<br />Overlapping (or non-overlapping) features can be located, and then marked as errors.<br />
    9. 9. node<br />B<br />node<br />C<br />Polygon<br />I<br />Polygon<br />III<br />node<br />A<br />Polygon<br />II<br />node<br />E<br />node<br />F<br />node<br />D<br />Polygon<br />V<br />Polygon<br />IV<br />node<br />G<br />Strict Topology<br />Features are composed from a common set of points and lines.<br />Altering the vertices of one polygon affects polygons that share those vertices. <br />Harder to introduce gaps or slivers.<br />
    10. 10. Topology<br />Can you think of a reason why topology would be important to model?<br />Where in the real world is this concept important?<br />Let’s take a look at some examples.<br />
    11. 11. Cadastre Example<br />survey (COGO)<br />parcels<br />zones<br />benchmark<br />
    12. 12. Parcel Overlap Example<br />The boundaries of two properties should never overlap, and there should never be a gap between them, unless intentional. <br />Clear error in parcel boundaries.<br />
    13. 13. Policy-based Topology Rules<br />In the NJ State Plan, CESs and the Environmentally Sensitive Planning Area both represent areas of environmental importance.<br />Thus, CESs should never be placed on top of the ES Planning Area.<br />In our utility network, poles hold up the transmission lines.<br />The transmission line features must always share a vertex with the utility pole point features.<br />
    14. 14. GIS is extensible<br />With modern GIS, a polygon is not just a polygon.<br />Software can be adapted to fit your model of reality.<br />The software can be easily extended to create new data types and perform new analyses. <br />GIS can be adapted to store, model, and display data about any observable phenomenon on the Earth.<br />
    15. 15. Objects<br />GIS Features as Objects is a recent method of representing aspects of the real-world in GIS<br />Example of the shift from specialty data to DBMS that are spatially-aware<br />Non-planar, temporally shifting, topologically linked, rule-based actions<br />Still important to check for topology to ensure as a quality control step<br />
    16. 16. Vector Geometry as Objects<br />Parcels<br />Planar geometries with attribute information<br />Parcels as objects in a Cadastral “carpet”<br />Objects with topology rules (“don’toverlap, unless”)<br />Members of “regional” features (zoning, municipality)<br />Composed of surveyed parts (COGO, benchmarks)<br />Keys that link to attribute tables (owner(s), assessments, plans, etc)<br />
    17. 17. Attributes as Objects<br />Not only can multiple sets of geospatial features interact with rules, the attributes can be linked with one another, with their own set of rules and actions<br />Ownership record linked to GIS parcel<br />Search on multiple owners, records<br />Removal of parcel warns about “orphan” owner<br />Functions that can be performed by GIS analyst can be embedded in the actual database<br />
    18. 18. Explore Models<br />Let’s take a look at several GIS data models.<br />Take note of the storage method:<br />Raster<br />Vector (and vector type: point, line, polygon, etc…)<br />Also take note of the model family:<br />Topological Model<br />Object Model<br />Both<br />
    19. 19. Elevation using LIDAR<br />LIDAR data is 3D elevation data recorded from an airplane. <br />Stored as “mass points” – even a small area is composed of thousands of point features.<br />No real need for attributes, simply XYZ points.<br />Points can be joined together to create a surface model of a landscape.<br />
    20. 20. Elevation DEMs<br />Digital Elevation Models, or DEMs, often refer to a raster representation of elevation. <br />Each cell in the raster grid contains a value that is the height of the cell above a fixed point (i.e. sea level).<br />
    21. 21. Elevation using TINs<br />Triangulated Irregular Networks, or TINs are vector models that represent elevation.<br />The study area is composed of individual triangles, composed of a network of shared nodes and edges<br />The surfaces of the triangles attempt to represent the surface, so in areas of gradual elevation change, there are fewer triangles.<br />
    22. 22. TIN Model of Campus<br />
    23. 23. TIN Model of Campus<br />
    24. 24. Networks<br />Analysis can be performed across a network, represented by a feature dataset of points and lines.<br />Road network or water, sewer, utility, rail, etc…<br />Optimal route – shortest, lowest cost, avoiding left turns, follow height and weight restrictions, time of day restrictions, include real-time traffic…<br />Multi-modal – walk/bike to bus stop, bus to train, walk from train to final destination.<br />
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    26. 26.
    27. 27. Models Diagrammed<br />GIS models can be depicted in a schematic form, similar to a flow chart.<br />Shows the interconnected nature of the classes that make up the overall model.<br />Some models can be constructed within ArcGIS using ModelBuilder.<br />
    28. 28.
    29. 29. NJ DEP Wastewater Model<br />
    30. 30. Creating GIS Models<br />Abstractions of reality naturally have shortcomings.<br />Models tailored to a specific task can be used to explore phenomenon or predict effects.<br />Developing a data model to solve a problem is how GIS has become a decision-making platform.<br />Consider how you could study an abstract set of data using GIS to solve real-world issues.<br />