GIS - the best way
to create
ugly maps
FAST
or GIS roots in Cartography
More bad maps…
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
Georeferencing
Is essential in GIS, since all information
must be linked to the Earth’s surface
 The method of georeferencing must be:

Unique, linking information to exactly one
location
 Shared, so different users understand the
meaning of a georeference
 Persistent through time, so today’s
georeferences are still meaningful
tomorrow

Georeferences as Measurements

Some georeferences are metric

They define location using measures of
distance from fixed places


Others are based on ordering


E.g., distance from the Equator or from the
Greenwich Meridian
E.g. street addresses in most parts of the
world order houses along streets
Others are only nominal

Placenames do not involve ordering or
measuring
Placenames

The earliest form of georeferencing


Many names of geographic features
are universally recognized


And the most commonly used in everyday
activities
Others may be understood only by locals
Names work at many different scales

From continents to small villages and
neighborhoods
Postal Addresses and Postcodes
Every dwelling and office is a potential
destination for mail
Dwellings and offices are arrayed along
streets, and numbered accordingly
Streets have names that are unique
within local areas
Local areas have names that are unique
within larger regions
If these assumptions are true, then a
postal address is a useful georeference
Where Do Postal Addresses Fail
as Georeferences?
In rural areas
Urban-style addresses have been extended
recently to many rural areas
For natural features
Lakes, mountains, and rivers cannot be
located using postal addresses
When numbering on streets is not
sequential
E.g. in Japan
Linear Referencing


A system for
georeferencing positions
on a road, street, rail, or
river network
Combines the name of
the link with an offset
distance along the link
from a fixed point, most
often an intersection
Users of Linear Referencing

Transportation authorities


To keep track of pavement quality, signs,
traffic conditions on roads
Police

To record the locations of accidents
Converting Georeferences

GIS applications often require
conversion of projections and ellipsoids


Street addresses must be converted to
coordinates for mapping and analysis


These are standard functions in popular
GIS packages
Using geocoding functions
Placenames can be converted to
coordinates using gazetteers
Latitude and Longitude

The most comprehensive and powerful
method of georeferencing


Metric, standard, stable, unique
Uses a well-defined and fixed reference
frame

Based on the Earth’s rotation and center of
mass, and the Greenwich Meridian
Latitude and the Ellipsoid
Latitude (of the blue
point) is the angle
between a perpendicular
to the surface and the
plane of the Equator
 WGS 84

Radius of the Earth at the
Equator 6378.137 km
 Flattening 1 part in

The “Unprojected” Projection

Assign latitude to
the y axis and
longitude to the x
axis



A type of cylindrical
projection
Is neither conformal
nor equal area
As latitude
increases, lines of
longitude are much
closer together on
the Earth, but are the

Also known as the Plate
Carrée or Cylindrical
Equidistant Projection
Map Projections
A map projection is a set of rules for transforming features from the
three-dimensional earth onto a two-dimensional display. No flat
representation of the earth can be completely accurate, so many
different projections have been developed, each suited to a
particular purpose. Map projections differ in the way they handle
four properties:
Area, Angles, Distance and Direction.
Rules:
1.
No projection can preserve all four simultaneously, although some combinations
can be preserved, such as Area and Direction
2.
No projection can preserve both Area and Angles, however. The map-maker
must decide which property is most important and choose a projection based on
that.
Learn more: http://mac.usgs.gov/mac/isb/pubs/MapProjections/projections.html
Map Projection
Different Plane Locations and
Viewpoints
Normal or Polar
Oblique
Transverse or
Equatorial
Different families of projections
azimuthal
cylindrical
conic
Distortion patterns
Universal Transverse
Mercator (UTM)
• Projection properties
– All Transverse properties
– Standard line is a meridian
– 60 zone divided
• Projection uses
– World Map
conformal
equal area
direction
distance
Robinson’s
projection
Uses tabular coordinates rather than mathematical formulas
to make the world "look right."
Directions true along all parallels and along central meridian
Distances constant along Equator and other parallels
Projection properties
•
Compromise
Projection uses
•
conformal
World atlas maps
equal area
direction
distance
State Plane Coordinates
Defined in the US by each state
Some states use multiple zones
Several different types of projections are
used by the system
Provides less distortion than UTM
Preferred for applications needing very
high accuracy, such as surveying
Mapping Lab
Geographic Data
Models and
GeoDatabases
Geographic Data Models
Vector and Raster - two main families
 Representation of geographic
information:

– Raster: location controlled, attribute
measured
 values
3
43
are stored in ordered array, so that
position in the array defines geographic
location
12 3
45
21
3
5
(v1,v2)
–
Vector:
attribute
controlled,
location
15 40 2 15
24
V
measured
10
64
 geographic
coordinates are stored separately
from attributes, connected with Identifiers
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 cell’s central point, or systematic
analigned
Legend
Mixed conifer
Douglas fir
Oak savannah
Grassland
Raster representation. Each color
represents a different value of a nominalscale field denoting land cover class.
The mixed pixel problem
Water dominates
Winner takes all
Edges separate
W W
G
W G
G
W
E
G
W W
G
W W
G
W
E
G
W W
G
W G
G
E
E
G
Methods of Grid Encoding
• point-based
• center point (regular grid) -DEMs, - but what if periodicity in
landscape?; what if pop. density?
• systematic unaligned (random in a cell)
• area-based
•
•
•
•
•
•
(have to integrate info...)
extreme value (max or min)
total (sum, like reflected light)
predominant type (most common)
presence/absence (binary result)
percent cover (% covered by single category)
precedence of types (highest ranking)
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 runlength encoding and quad trees.
Rasters and vectors can be flat files
… if they are simple
Vector-based line
Raster-based line
Flat File
4753456
4753436
4753462
4753432
4753405
4753401
4753462
4753398
623412
623424
623478
623482
623429
623508
623555
623634
Flat File
0000000000000000
0001100000100000
1010100001010000
1100100001010000
0000100010001000
0000100010000100
0001000100000010
0010000100000001
0111001000000001
0000111000000000
0000000000000000
Compacting Raster

from simple matrix to...
...run-length encoding
...row differences encoding, TIFF
...Quadtrees, Morton numbers
0
203
1
3
1
21
Vector - Land Records
Surveyed feature
20.37’
26.23’
13
12
30.5’
26.23’
GIS
Survey
Link
/
Survey point
/
/
/
/
/
9
Computation
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, polygon
shading is easy, IF CORRECT!
– problems: common line defined twice;
slivers between adjacent polygons
because boundaries not
necessarily the same
(x1,y1)
(x2,y2)
(x3,y3)
(x5,y5)
(x4,y4)
(x6,y6)
Vector Data Structure Alternatives 2

Point dictionary
– polygon descriptions refer to lists of fixed
points with coordinates (point dictionaries)
– similar to polygon loops, but instead of
coordinates of vertices in polygon
descriptions - IDs of vertices

Topological data structure
1
2
3
5
4
– Organizes Points, Lines, and Areas as
Nodes, Chains, and Polygons
– The model: nodes bound chains, chains co-bound polygons;
chains 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...
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
Basic arc topology
3
n2
2
A
1
n1
B
Topological Arcs File
Arc
1
From To PL PR n1x n1y n2x n2y
n1 n2 A B x y
x y
Tracking Topological Relationships

Connectivity
– nodes bound chains
– chains bound polygons
in turn,
– chains are bounded by nodes
– polygons are bounded by chains
Node table
ID
1
2
3
4
1
III
2
B
3
IV
A
I
U
II
V
C
VI
4
Point table
ID
a
b
c
d
…
Chains
<list>
<list>
<list>
<list>
Polygon table
ID Chains
A
<list>
B
<list>
C
<list>
U
<list>
Coord
<x,y>
<x,y>
<x,y>
<x,y>
<…>
Chain table
ID
I
II
III
IV
V
VI
Vertices
<list>
<list>
<list>
<list>
<list>
<list>
From
1
1
1
3
4
2
To
4
2
3
2
3
4
Left
A
U
B
B
A
U
Right
U
B
A
C
C
C
Typical Digitizing Situations
this is ideal, but...
undershoot,
and what to do
overshoot, and what
to do with it
Planar Enforcement Is Not Enough
• Interrelationships between semantic and spatial
structures
Each string is marked with
left and right labels
Trying to assemble polygons
from these strings: there may
be 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
Automatic labeling results…
3
4
1
2
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

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
Spatial Types – OGC Simple Features
Geometry
Point
SpatialReferenceSystem
Curve
Surface
LineString
Polygon
Line
LinearRing
Composed
Type
Relationship
GeometryCollection
MultiSurface
MultiCurve
MultiPolygon
MultiLineString
MultiPoint
Elements of a Geodatabase
Geometric Network
Feature Dataset
Relationship Class
Feature Class
Annotation Class
Object Class
The Geodatabase Data Model
Feature Datasets
Container
Same spatial reference
Analogous to a coverage
The Geodatabase Data Model
Object and Feature Behavior
End users and data modelers can :
• Instantiate classes with predefined behavior
• Control the default value and acceptable values
for any attribute in a class (domains)
• Partition the objects in a class into like groups
(subtypes)
• Control the general and network relationships in
which an object can participate
Rule based, no programming required
The Geodatabase Data Model
Validation Rules
Attribute domains
Connectivity rules
Relationship rules
... are stored in the Geodatabase
Custom rules
... are code based
The Geodatabase Data Model
Domains in ArcMap
Attribute editor uses domain values
Identifies illegal values
Provides legal value lists
The Geodatabase Data Model
Pole Attachments
Composite relationship: pole to transformer
Select a pole and move it
…the transformer follows
The Geodatabase Data Model
Geometric Networks
Feature Classes
Valve
Geometric Network
Service
Feed
Lateral
Main
The Geodatabase Data Model
Direct Multi User Editing
Editor A
Editor B
Editor C
Editing, Long Transaction and Versioning
Conflict Resolution
Conflicts are automatically detected
Conflicting
FeatureClass
Conflicting feature(s)
Options to resolve conflict
Versions
Conflicting
field
Editing, Long Transaction and Versioning
Spatial Relations
Equals – same geometries
Disjoint – geometries share common point
Intersects – geometries intersect
Touches – geometries intersect at common
boundary
Crosses – geometries overlap
Within– geometry within
Contains – geometry completely contains
Overlaps – geometries of same dimension
overlap
Relate – intersection between interior,
boundary or exterior
Contains Relation
Touches Relation
Spatial Methods
Distance – shortest distance
Buffer – geometric buffer
ConvexHull – smallest convex polygon
geometry
Intersection – points common to two
geometries
Union – all points in geometries
Difference – points different between two
geometries