GIS - - the best way to create ugly maps FAST

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GIS - - the best way to create ugly maps FAST
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More bad maps
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Representing and Transforming

• Graphic symbols
• size, symbology, value, saturation, shape,
  arrangement, texture, focus
• Classification procedures are used to ease user
  interpretation
• Natural, quantile, equal interval, s.d.
• Cartogram transformations distort area or
  distance for some specific reason

More examples US Transportation Survey
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(No Transcript)
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Components of Geographic Information
Theme
Time
Space
Points
Lines
Areas
Volumes
Nominal
Ordinal
Interval
Ratio
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(A Start at) a Typology of Thematic Maps

• fixed controlled measured
• geological time theme location
• map
• census data time location theme
• weather location time theme
• report
• tide table theme location time
• flood hydro. location time theme
• grid cell data time location theme

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Geographic Data Models

• Vector and Raster - two main families
• Representation of geographic information
• Raster location controlled, attribute measured
• values are stored in ordered array, so that
  position in the array defines geographic location
• Vector attribute controlled, location measured
• geographic coordinates are stored separately from
  attributes, connected with Identifiers

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Rasters

• How to represent phenomena conceived as fields or
  discrete objects?
• Raster
• Divide the world into square cells
• Register the corners to the Earth
• Represent discrete objects as collections of one
  or more cells
• Represent fields by assigning attribute values to
  cells
• More commonly used to represent fields than
  discrete objects
• Characteristics
• Pixel size
• The size of the cell or picture element, defining
  the level of spatial detail
• All variation within pixels is lost
• Assignment scheme
• The value of a cell may be an average over the
  cell, or a total within the cell, or max, or min,
  or the commonest value in the cell, or
  presence/absence, or
• It may also be the value found at the cells
  central point, or systematic analigned

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Legend
Mixed conifer
Douglas fir
Oak savannah
Grassland
Raster representation. Each color represents a
different value of a nominal-scale field denoting
land cover class.
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The mixed pixel problem
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RASTERS

• Each cell can be owned by only one feature.
• Rasters are easy to understand, easy to read and
  write, and easy to draw on the screen. A grid or
  raster maps directly onto an array.
• Grids are poor at representing points, lines and
  areas, but good at surfaces.
• Grids are a natural representation for scanned or
  remotely sensed data.
• Grids suffer from the mixed pixel problem.
• Grid compression techniques used in GIS are
  run-length encoding and quad trees.

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Rasters and vectors can be flat files if they
are simple
Flat File
Vector-based line
4753456 623412
4753436 623424
4753462 623478
4753432 623482
4753405 623429
4753401 623508
4753462 623555
4753398 623634
Raster-based line
Flat File
0000000000000000
0001100000100000
1010100001010000
1100100001010000
0000100010001000
0000100010000100
0001000100000010
0010000100000001
0111001000000001
0000111000000000
0000000000000000
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Compacting Raster

• from simple matrix to...
• ...run-length encoding
• ...row differences encoding, TIFF
• ...Quadtrees, Morton numbers

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Vector - Land Records
Surveyed feature
20.37
26.23
R 10
45.81
45.81
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35.44
30.5
26.23
GIS
Survey
Link
/
/
/
Survey point
/
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/
/
Computation
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Vector Data Structure Alternatives 1

• Development trends
• increasing complexity, refining logic
• making geographic relationships EXPLICIT
• Spaghetti files (1974...)
• the original CIA format
• lines and points which the reader must organize
• Polygon loops (location lists)
• polygons stored as objects, polygonshading is
  easy, IF CORRECT!
• problems common line defined twice slivers
  between adjacent polygons because boundaries not
  necessarily the same

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Vector Data Structure Alternatives 2

• Point dictionary
• polygon descriptions refer to lists of
  fixedpoints with coordinates (point
  dictionaries)
• similar to polygon loops, but instead of
  coordinates of vertices in polygon descriptions
  - IDs of vertices
• Topological data structure
• Organizes Points, Lines, and Areas as Nodes,
  Chains, and Polygons
• The model nodes bound chains, chains co-bound
  polygonschains co-bound nodes, polygons
  co-bound chains...
• the structure stores topological relationships
  between nodes, chains, and polygons these
  relationships are used in defining chains through
  nodes, polygons through chains, etc.
• Provides for contiguity, better quality
  control...

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Topology

• TOPOLOGY study of basic spatial relationships
  based on intuitive notions of space (those not
  requiring numerical measurements) fundamental
  level of mathematics of space
• Topology IS NOT topography
• TOPOGRAPHY measurement/representation of earth
  elevation and related features (a form of
  general/ reference map)
• Why topology in cartography/GIS
• lines are coded once - avoids redundancy
• data quality issue topo-logical consistency

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Basic arc topology
n2
3
2
A
1
B
n1
Topological Arcs File
Arc
From
To
PL
PR
n1x
n1y
n2x
n2y
1
n1
n2
A
B
x
y
x
y
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Arc/node map data structure with files
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1 x y
11
e
2 x y
l
i
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3 x y
F

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2
s
4 x y
t
7
n
5 x y
i
5
o
POLYGON A
6 x y
P
9
7 x y
4
8 x y
6
1
9 x y
2
10 x y
3
11 x y
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12 x y
13 x y
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File of Arcs by Polygon
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1,2,3,4,5,6,7
A
1,2
, Area, Attributes
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1,8,9,10,11,12,13,7
Arcs File
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Tracking Topological Relationships

• Connectivity
• nodes bound chains
• chains bound polygons
• in turn,
• chains are bounded by nodes
• polygons are bounded by chains

U
1
2
3
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Point table
Node table
ID Coord a ltx,ygt b ltx,ygt c
ltx,ygt d ltx,ygt ltgt
ID Chains 1 ltlistgt 2 ltlistgt 3
ltlistgt 4 ltlistgt
Chain table
ID Vertices From To Left Right I ltlistgt 1 4 A U II
ltlistgt 1 2 U B III ltlistgt 1 3 B A IV ltlistgt 3 2 B
C V ltlistgt 4 3 A C VI ltlistgt 2 4 U C
Polygon table
ID Chains A ltlistgt B ltlistgt C
ltlistgt U ltlistgt
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Typical Digitizing Situations
overshoot, and what to do with it
this is ideal, but...
undershoot, and what to do
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Planar Enforcement Is Not Enough

• Interrelationships between semantic and spatial
  structures

Each string is marked withleft and right
labelsTrying to assemble polygonsfrom these
strings there maybe more than one label to
the left of all strings forming a closed
polygon a standard topological error...
However, these labels may be in container
relationship in a domain map
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Automatic labeling results
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Special Cases 1

• B basal nucleus of Meynert (C0004788)
• LGP lateral globus pallidus, C0262267
• Basal nucleus cells (B) are within LGP, but their
  precise locations not known ? polygon is coded
  LGP, B is a secondary descriptor

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Special Cases 3

• DG dentate gyrus, C0152314
• PoDG polymorph layer of the dentate gyrus
• CA1 field CA1 of hippocampus (C0019564)
• All of them have a common parent hippocampus ? a
  common parent is used to label polygon polylines
  are labeled separately