Winter 2011 GIS Institute
Space:
Questions & Tools
Space: Questions
• Questions can range from basic to complex:
– How does a variable or phenomenon vary over
space? (Can be answered with a map)
– How does distance to public transportation
affect house values? (Can be answered using
traditional statistical software, with spatial
variables created using GIS)
– What is the spatial distribution of foreclosures
in Phoenix, AZ? (Can be answered with maps
and descriptive spatial statistics)
– What is the impact of foreclosure densities on
neighborhood crime? (Can be answered with
spatial statistics and models)
Winter 2011 GIS Institute
Space: Tools
• As with any other discipline, geographers
work with a range of “spatial” questions,
and there are generally myriad
approaches with which to answer those
questions
• This week we will focus primarily on
developing your comfort level with GIS,
Geographic Information Systems
– Commonly used for data collection,
management, mapping, and analysis
Winter 2011 GIS Institute
What is GIS?
• Geographic Information Systems or Science
– A bringing together of skills, theory, computer
science, database management, and geography
– A collection of:
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Hardware
Software
Data
People
Procedures
Network
– An abstraction of reality
Rachel Franklin
Clarke (2001) presents the following
definitions:
• GIS is “a powerful set of tools for
storing and retrieving at will,
transforming and displaying spatial
data from the real world for a
particular set of purposes.”
– Burrough, 1986
Rachel Franklin
• GISs are “automated systems for the
capture, storage, retrieval, analysis,
and display of spatial data.”
– Clarke, 1995
Rachel Franklin
• A GIS is “an information system that
is designed to work with data
referenced by spatial or geographic
coordinates. In other words, a GIS is
both a database system with specific
capabilities for spatially-referenced
data, as well as a set of operations
for working with the data.”
– Star and Estes, 1990
Rachel Franklin
• GIS is “a special case of information
systems where the database consists of
observations on spatially distributed
features, activities, or events, which
are definable in space as points, lines,
or areas. A geographic information
system manipulates data about these
points, lines, and areas to retrieve data
for ad hoc queries and analyses.”
– Dueker, 1979
Rachel Franklin
• GIScience is “the generic issues that
surround the use of GIS technology,
impede its successful
implementation, or emerge from an
understanding of its potential
capabilities.”
- Goodchild, 1992
Rachel Franklin
Source: krygier.owu.edu
Source: sutton.gov.uk
Roles of a GIS (Fotheringham)
• Data manipulation
• Data integration
– Using GIS to create new information that
is then used in other software or analysis
environments
• Data visualization
– For example, looking at regression
residuals
Winter 2011 GIS Institute
A brief history of GIS
• Cartography, especially thematic maps
• Map overlay
– Tyrwhitt’s 1950 chapter in Town and Country
Planning Textbook
– McHarg’s 1969 Design with Nature
Source: architectmagazine.com
Brief History Continued…
• The Canada Geographic Information
System, mid-1960s
• The Census Bureau’s DIME (Dual
Independent Map Encoding), late 1960s
• Computerized cartography
• Freestanding GIS software packages
• Ever-increasing computer power
• Ever-increasing quantities of spatial data
Rachel Franklin
What can we do with a GIS?
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Make maps
Compute summary statistics
Import, manipulate, and manage data
Spatial analysis
Rachel Franklin
Early example of spatial analysis:
John Snow’s 1854 Cholera Map
Other Examples
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Habitat suitability
Hurricane vulnerability
Heat wave vulnerability
Bus stop locations
Smart growth policies
Rachel Franklin
Nice Maps
Winter 2011 GIS Institute
Interactive Maps
http://www.washingtonpost.com/wp-srv/special/politics/2010-race-maps/house/
http://www.mappiness.org.uk/
Rachel Franklin
What do you think of this map? The analysis?
Rachel Franklin
Or this one? (Hint: sometimes our spatial research
challenges in aren’t necessarily cartographical)
Traditional Spatial Analysis, Redux
• Tobler’s First Law of Geography states that,
“Everything is related to everything else,
but near things are more related than
distant things.”
• Geographers and others have often try to
measure the “everything is related to
everything else” by looking at connections
between pairs of locations or entities
– Provides clues about diffusion behaviors, as well
as strength of ties between places
– e.g. migration flows, commuter flows,
communication flows
Winter 2011 GIS Institute
Regionalization
• MIT’s SENSEABLE
City Lab used
telephone call data
from British
Telecom to redraw
the regional map
of Great Britain.
Winter 2011 GIS Institute
Traditional Spatial Analysis, Redux
Winter 2011 GIS Institute
Organizing Spatial Data in a GIS
• A GIS doesn’t save information as maps
– Rather, we tell the GIS how to locate objects
in relation to other objects and in space
• Things to be aware of:
– Your spatial data model
– The relationships your objects have with
each other in the real world
• e.g. street intersections or shared state borders
• We call this “topology”
Winter 2011 GIS Institute
Spatial Data Models
• Most common are vector and raster
Polygon
Point
Line
Vector
Raster
Winter 2011 GIS Institute
Vector Model
• Features are stored as points, lines or polygons
– All are combinations of nodes and vertices
• Locations are recorded as X,Y coordinates
• Each feature – point, line, or polygon – is linked
to an “attribute table” or set of variables
– For example, you could have a dataset of cities,
represented as points, and the attribute table might
contain characteristics of the city – population,
median household income, etc.
• Feature classes – or datasets of spatial objects –
contain only the same types of objects
– This means only points or lines or polygons
– And since they all share the same attribute table,
they should be the same thing
• So, no combining cities and septic systems in one feature
class, even though both might be points
Winter 2011 GIS Institute
Why We Like the Vector Model
• Features can be located precisely
• We can store lots of information
(variables or attributes) about each
feature
• Useful for many types of map-making
• Perfect for types of analysis, such as
areas, lengths, or connections
Winter 2011 GIS Institute
Raster Data Model
• Sub-divides a study area into square
pixels – rows and columns
• Only need the location of the upper lefthand corner and all other locations are
implicit, assuming you know your pixel
size
• Only one value is recorded for each pixel
– For example, temperature, precipitation, or
land use type
Winter 2011 GIS Institute
Why We Like the Raster Model
• Best for continuous data
• Analysis can sometimes be faster
• And some types of analysis require
raster data
• “Yes, raster is faster, but raster is
vaster, and vector just seems more
correcter.” – Dana Tomlin
Winter 2011 GIS Institute
Topology – Modeling Feature Behavior
• Topology sets the rules of behavior for
features in a feature class
• A classic example is road networks:
Highway Overpass
Typical Street Corner
• Basic topology rules deal with adjacency,
connectivity, overlap, and intersection
Winter 2011 GIS Institute
The End…for Now…
• Let’s go see the computer lab
• And break for lunch
• We’ll reconvene at 1:00 pm in CIT 265
Winter 2011 GIS Institute