Representation of spatial data. GIS thematic layers, raster and vector, conversi on , subdivisi on representation, continu ous data: contours, DEMs, TINs. Thematic map la yers. Separate storage of data according to them e : map la yers
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GIS thematic layers, raster and vector, conversion, subdivision representation, continuous data: contours, DEMs, TINs
Census data, 1995
Example: CountrymapofSouth America
Geometry: coordinatesof the bordersTopology: whichcountries border which Attributes: namesofcountries, population, etc.
Point object in
Line object in
Plane object in
Obtained after scanning, remote sensing
Less suitablefor point and line objects: representationdoes not follow intuition
Not adaptive: no difference in detail possible in different regions
Eitherexpensive in memory, orlittle precision
Not obtained after digitizingRaster: pros and cons
(34,67) forest 9
(34,67) forest 4,6
Small storage consumption
Adaptive: additional controlpointspossible
Network and clusteranalysispossible
Obtained after digitizing
Map overlay and buffer computation complexVector: pros and cons
C1: (..,..), (..,..), (..,..), ...
C2: (..,..), (..,..), (..,..), ...
C3: (..,..), (..,..), (..,..), ...
P1: (..,..), (..,..), (..,..), ...
P2: (..,..), (..,..), (..,..), ...
P3: (..,..), (..,..), (..,..), ...
Doubly-connected edge list
Doubly-connected chain list
E.g. for data integration
DP-standard(i, j, )
Determine farthest point pkbetween piandpj
Ifdistance(pk, pi pj) > then DP-standard(i, k, )
DP-standard(k, j, )
Return the concatenationof
Solution: test output forself-intersectionsand continue adding controlpoints if necessary
DP-improved(i, j, )
Simp = DP-standard(i, j, )
V = set ofintersecting segmentsofSimpRepeat
For all segments s VRefine(s) in Simp Do 1 refinementà la DP by adding the farthest pointV = set of intersecting segmentsofSimpUntilV is empty
Digital Elevation Model (DEM)
Triangulation(TIN; triangulatedirregular network)
Because t1 has pointers to two the same vertices as t, we can determine their shared edge, even though it is not represented explicitly