Coordination of geographic information and geographic information systems Metadata
Geographic Information Systems
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Transcript of Geographic Information Systems
1. Components of Geographic 1. Components of Geographic DataData
Spatial locations Attributes Topology Time
Components – Spatial LocationsComponents – Spatial Locations
Specified with reference to a common coordinate system
points lines polygons volumes
grids
Components - AttributesComponents - Attributes
Nominal - qualitative, e.g., grasses, trees, buildings,
Ordinal - rankble quality, e.g., high, medium, low
Interval
- quantitative but not ratio, e.g., 400F, 800F
Ratio
- absolute quantities, e.g., , e, -96.345, …
ComponentsComponents
Topology
Spatial relationship between geographic features
Adjacency
Containment
Connectivity
etc.
Time
Presently treated as an attribute
Data Models – Objects and FieldsData Models – Objects and Fields
Objects and Field View
Objects
- Are discrete or have identifiable boundaries
- Have attributes
Field
- Varies continuously
- Has no obvious boundaries
Data ModelsData Models
Vector data model Raster data model
courtesy: Mary Ruvane, http://ils.unc.edu/
Data Models - (1) VectorData Models - (1) Vector
Every position has a pair of coordinates. Lines and polygons are constructed by
connecting a series of points. Points, lines, and polygons are used to represent
geographic features.
Epidemiological Studies- Disease TrackingEpidemiological Studies- Disease Tracking
Incidence of Viruses
ESRI, GE SmallWorld
using the land-cover map and field snail survey including 93 positive snail sites and 800 non-positive snail sites
0 3,300 6,6001,650 Meters
±
Positive snail
0.00 - 0.03
0.04 - 0.13
0.14 - 0.23
0.24 - 0.33
0.34 - 0.60
Lake
Positive Snail Prediction of Xichang Study Site
Data Models - (2) RasterData Models - (2) Raster
A matrix consists of regular grid cells Positions are defined by column and row numbers Each cell has a single value
Data Models - (2) RasterData Models - (2) Raster Data consists of mostly attributes A header file stores (1) Number of rows and columns, (2)
Cell size, and (3) Coordinates of the origin Coordinates of a location can be converted on the fly
2 Data Model2 Data Model
(3) Advantages and Disadvantages(3) Advantages and Disadvantages Raster Vector
Ad and Disad - RasterAd and Disad - Raster
Advantages
- It is a simple data model - Overlay operation can be easily implemented - High spatial variation is efficiently represented
Disadvantages
- It is less compact- Topological relationships are difficult to
represent - The output is less aesthetically pleasing
Ad and Disad - VectorAd and Disad - Vector
Advantages
- It is a compact data model - It is efficient in coding topology
- The output closely approximate hand-drawn maps
Disadvantages
- It is a complex data model - Overlay operations are difficult to implement - The representation of high variation is inefficient
GIS Data StructuresGIS Data Structures
Raster data structures
- Run length - Quadtrees
Vector data structures
- Non-topological structure
- Topological structure
3 Raster Data Structures3 Raster Data Structures(1) Run Length(1) Run Length
Data are recorded in the order of
Attribute1, number of cells in the run;
Attribute2, number of cells in the run; …
3 Raster (1) Run Length3 Raster (1) Run Length
11,4; 3,4;
11,4; 3,4;
11,4; 3,4;
11,4; 3,4;
11,3; 3,1; 5,4
…
11 11 11 11 3 3 3 3
11 11 11 11 3 3 3 3
11 11 11 11 3 3 3 3
11 11 11 11 3 3 3 3
11 11 11 3 5 5 5 5
11 11 5 5 5 5 5 5
11 11 5 5 5 5 5 5
11 11 5 5 5 5 5 5
3 Raster Data Structures3 Raster Data Structures(2) Quadtrees(2) Quadtrees
Subdividing a region into quadrants until each quadrant contains only one class - variable resolution
4 Vector Data Structures4 Vector Data Structures(1) Non-topological Structure(1) Non-topological Structure
There is no topology and shared boundaries are recorded twice
4 Vector (1) Non-Topological 4 Vector (1) Non-Topological StructureStructure
Storing coordinates of
two polygons: and
Polygon
x1, y1; x2,y2; x3,y3; …. x1,y1.
Polygon
x1, y1; x2,y2; x3,y3; …. x1,y1.
(x1, y1) (x1, y1)
(x2, y2) (x2, y2)
A
B
1 2
1 2
1
2
4 Vector (2) Topological Structure4 Vector (2) Topological Structure No node or line segment is duplicated Line segments and nodes can be referenced to more than
one polygons All polygons have unique identifiers Island and hole polygons can be uniquely represented
4 Vector (2) Topological Structure4 Vector (2) Topological StructureStoring coordinates of two polygons: and
Line 1
x1, y1; x2,y2; x3, y3; x4, y4; x5,y5; Line 2
x1, y1; x2,y2; Line 3
x1, y1; x2,y2; x3, y3; x4, y4;
Polygon Line 1, Line 2Polygon Line 2, Line 3
(x1, y1) (x1, y1)
(x2, y2) (x2, y2)
1 2
1 2
1
2
Line 1
Line 2
Line 3
4 Vector (2) Topological Structure4 Vector (2) Topological Structure Polygon = a list of lines Line = a set of coordinates
Topological- the Arc-Node ModelTopological- the Arc-Node Model
Arc - a line starting and ending at a node Node - intersection point where two or more arcs
meet
or it is a dead end Polygon - a closed chain of arcs
Arc-Node ModelArc-Node Model
Polygon topology table Node topology table Arc topology table
Arc coordinate data table