Collection Data Techniques
Raster
Vector
Secondary
Digitalremote
sensingimages
GPS
measurements
Digitalaerial
photographs
Primary
Survey
measurements
Scannedmaps
Topographic
surveys
DEMsfrommaps Toponymydata
setsfromatlases
Primary Data Capture
Capture specifically for GIS use
Raster remote sensing
e.g. SPOT and IKONOS satellites and aerial
photography
Passive and active sensors
Resolution is key consideration
Three key aspects of resolution:
Spatial
Spectral
Vector Primary Data Capture
Surveying
Locations of objects determines by angle and
distance measurements from known locations
Uses expensive field equipment and crews
Most accurate method for large scale, small areas
GPS
Collection of satellites used to fix locations on Earths
surface
Differential GPS used to improve accuracy
Secondary Geographic Data
Data collected for apture
C other purposes can be
converted for use in GIS
Raster conversion
Scanning of maps, aerial photographs,
documents, etc
Important scanning parameters are spatial
and spectral (bit depth) resolution
Vector Secondary Data Capture
Collection of vector objects from maps,
photographs, plans, etc.
Digitizing
Manual (table)
Heads-up and vectorization
Photogrammetry the science and technology
of making measurements from photographs, etc.
COGO Coordinate Geometry
Managing Data Capture
P
Key principles rojects
Fundamental tradeoff between
Clear plan, adequate resources, appropriate funding,
and sufficient time
Quality, speed and price
Two strategies
Incremental
Blitzkrieg (all at once)
Alternative resource options
In house
Specialist external agency
Summary
Data collection is very expensive, timeconsuming, tedious and error prone
Good procedures required for large scale
collection projects
Main techniques
Primary
Raster e.g. remote sensing
Vector e.g. field survey
Secondary
Raster e.g. scanning
Vector e.g. table digitizing
Addendum:
Volunteered
The Tea Fire
Geographic
Santa
Information
Barbara,
(VGI)
California,
Nov. 2008
An unfortunate
case study
Exacerbated
by
sundowner
VGI: An
unfortunate
The Tea Fire
case study
Official sources:
Precise fire boundaries
every 24-36 hours
GIS and Image-based
techniques
PDF format, posted
online and distributed
at community outlets
Unofficial sources
Rough boundaries
Real-time
Volunteered Geographic
Information (VGI) @
GMU
30,000+ students
Majority geo-aware and
with mobile computing
Could they be used to
augment an official
information source with
VGI?
Goal:
Capture real-time VGI-
Building VGI @
GMU: GeoParsing
Collect available
sources of official
infrastructure data
building footprints
building contents
sidewalks, roads,
parking
Build a localized
gazetteer
Develop ability to geo-
A Localized
Gazetteer
Purpose:
.
Translate between human
world and GIS world
provide spatial footprint for
placenames in VGI
Link resources by location
Current problem with
campus emergency alert
system: Ambiguous
Gazetteer
Digital Representation
Uses only two symbols, 0 and 1, to represent
information
The basis of almost all modern human
communication
Many standards allow various types of
information to be expressed in digital form
MP3 for music
JPEG for images
ASCII for text
GIS relies on standards for geographic data
Types of Attributes
Nominal, e.g. land cover class
Ordinal, e.g. a ranking
Interval, e.g. Celsius temperature
Ratio, e.g. Kelvin temperature
Differences make sense
Ratios make sense
Cyclic, e.g. wind direction, slope
Cyclic Attributes
Do not behave as other
attributes
What is the average of two
compass bearings, e.g. 350 and
10?
Occur commonly in GIS
Slope aspect
Wind direction
Flow direction
Special methods are needed
The Fundamental Problem
Geographic information links a place, and often
a time, with some property of that place (and
time)
The temperature at 34 N, 120 W at noon local time
on 12/2/99 was 18 Celsius
The potential number of properties is vast
In GIS we term them attributes
Attributes can be physical, social, economic,
demographic, environmental, etc.
The Fundamental Problem
contd.
The number of places and
times is also vast
The more closely we look at the
world, the more detail it reveals
Potentially infinite
Potentially ad infinitum
The geographic world is infinitely
complex
Humans have found ingenious
ways of dealing with this
problem
Many methods are used in GIS to
create representations or data
models
Discrete Objects
Points, lines, and areas
Countable
Persistent through time, perhaps mobile
Biological organisms
Animals, trees
Human-made objects
Vehicles, houses, fire hydrants
Continuous Fields
Properties that vary continuously over space
Value is a function of location
Property can be of any attribute type, including
direction
Elevation as the archetype
A single value at every point on the Earths surface
The source of metaphor and language
Any field can have slope, gradient, peaks, pits
Characteristics of Rasters
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 the commonest value in
the cell
It may also be the value found at the cells central
point
Vector Data
Used to represent points, lines, and areas
All are represented using coordinates
One per point
Areas as polygons
Straight lines between points, connecting back to the start
Point locations recorded as coordinates
Lines as polylines
Straight lines between points
Raster vs Vector
Volume of data
Raster becomes more voluminous as cell size
decreases
Source of data
Remote sensing, elevation data come in raster form
Vector favored for administrative data
Software
Some GIS better suited to raster, some to vector
GIS
software
Chapter 7, parts of a GIS
4 technical parts:
Network
Hardware
Software
Data
GIS Software: The processing of engine a complete,
working, GIS
Narrower view of GIS software:
Systems with a range of generic capabilities to
collect, store, manage, query, analyze, and present
geographic information
Distributed primarily as commercial-off-the-shelf
Architectur
e of GIS
Software
Fig. 7.2
Three-tier
perspective on
GIS software
(using
terminology
from
Information
Systems)
Architectur
e of GIS
Software
Centralized
desktop GIS
(fig.7.5)
Thin clients
are used to
run only a
small
application,
that
Desktop &
Network
Todays
GIS
Geographic
nformation
pIaradigms
Systems
work with
software
running on
the desktop
or on the
web.
GIS
Software
Systems &
Vendors
Types of
GIS
Software
Main types of GIS software:
Desktop GIS
Web Mapping
Server GIS
Virtual Globes
Developer GIS
Hand-held GIS
Desktop GIS:
Software ported to PCs (mid-90s)
Desktop GIS is now the most widely-used category
of GIS software systems
From Professional high-end editor-analysis
systems: ESRI ArcInfo, Intergraph GeoMedia
Types of
GIS
Software
Main types of GIS software:
Desktop GIS
Web Mapping
Server GIS
Virtual Globes
Developer GIS
Hand-held GIS
Web Mapping:
2000-2010
Integrated Web-accessible software
2-D map database and services (routing,
gazetteers, etc.)
Google Maps, MyMaps
Types of
GIS
Software
[p.167-174]
Main types of GIS software:
Desktop GIS
Web Mapping
Server GIS
Virtual Globes
Developer GIS
Hand-held GIS
Server GIS:
Last decade 1990s dominated by desktop
GIS, next decade will be dominated by
Server GIS products.
Server GIS runs on a computer server that
can handle concurrent processing requests
Types of
GIS
Software
Main types of GIS software:
Desktop GIS
Web Mapping
Server GIS
Virtual Globes
Developer GIS
Hand-held GIS
Virtual Globes:
3-D Web services hosted on Web-based
GIS that publish global 3-D databases and
associated services for use over the Web.
[p.200]
Global 3-D databases
3-D web services
Types of
GIS
Software
Main types of GIS software:
Desktop GIS
Web Mapping
Server GIS
Virtual Globes
Developer GIS
Hand-held GIS
Developer GIS:
GIS Vendors release collections of GIS
software components for developers.
Toolkits of GIS Functions for programmers
to use in building GIS applications
http://www.deluoelectronics.com/customer/154-Deluo_Marine_Navigation_System
Examples: BlueMarble Geographics
GeoObjects, ESRI ArcGIS Engine, MapInfo
MapX
Types of
GIS
Software
Main types of GIS software:
Desktop GIS
Web Mapping
Server GIS
Virtual Globes
Developer GIS
Hand-held GIS
Handheld GIS:
Handheld GIS are lightweight systems designed
for mobile and field use
Important factors in development:
Miniaturization & hardware design
Introduction
Atomic Element of Geographic Information
Location (X , Y) , Time , Attribute
Time is an optional element in geographic information,
but location is essential
Terms used to describe the act of assigning location
to atoms of information:
georeference
geolocate
geocode
Georeferences
Every georeference
has an associated
spatial resolution
equal in size to the size
of the area that is
assigned that
georeference.
Street address
assigned to a parcel
by a municipality,
passed on to tax
assessor, EMS,
schools, etc.
Georeferences
Metric georeferences, such as
latitude and longitude are
based on measurement.
Advantage: infinitely fine spatial
resolution with finer
measurement
Advantage: GIS functionality,
including computing distance
Metric georeferences are
much more useful because
they allow maps to be made
and distances to be calculated
Georeferen
cing:
Gazetteer:
Placename
s
A geographic
dictionary or
index
Link between
a placename
and a map
Alexandria Digital
Library Gazette Server
Client
UCSB Map & Imagery
Library / UC Board of
Regents
Georeferen
cing:
Cadasters
and the US
Public
Land
Survey
System
Cadaster: A map of land
ownership for taxing land and for
public record
Parcels of land organized in a
cadaster and uniquely identified
and persistent, therefore a good
means of georeferencing land.
US Public Land Survey System
was developed during the
settlement of the western US
A Surveyor lays out a NorthSouth meridian, then 6 mile by 6
mile blocks referenced by
township and range index
numbers. Each section is divided
further into 36 1 mile by 1 mile
sections, and further into four
Projections
and
A basic problem
Ccoordinate
aused by a
round Earth:
s
Earth: Ellipsoid
Paper: Flat
Maps: Flat
Photographic
film: Flat
Map
projections
Map projects always distort the
Earth in some way, but some map
projections are good at
preserving certain characteristics
or properties. Two important map
properties are conformality and
equivalence.
Conformal projections preserve
shape of small features, and
preserves angles locally. The
scale of the projection is the
same in any direction. Because
conformal projections are good at
preserving angle (bearing) they
are often used for navigation.
Examples:
Mercator Projection (1569)
Lambert Conformal Conic (1772)
Map
projections
Equal Area
(Equivalent)
projections
preserve
area. Areas
measured on
the map are
always in the
same
Map
projections
Cylindrical
projections
are
analogous to
wrapping a
cylindrical
sheet of
paper around
Map
projections
Azimuthal or
planar
projections
are
analogous to
touching the
Earth and
projecting its
Map
projections
Conic
projections
are
analogous to
wrapping a
sheet of
paper in a
cone shape
Map
Projections:
Plate Care
The Plate
Care (or
Cylindrical
Equidistant)
projection
simply
assigns X to
longitude and
Y to latitude
Map
Projections
: UTM
The Universal
Transverse
Mercator
Projection
(abbreviate
UTM) is used in
many military
applications and
datasets with
national or
Map
Projections
: UTM
UTM
coordinates are
in meters, with
extra decimals
for sub-meter
precisions:
855,000
meters east
Map
Projections
The State
: State
Plane
Plane
Coordinate
System
Coordinate
(SPCS)
aSystem
llows for
(SPCS)
measuremen
ts that can be
more
accurate than
with UTM.