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GIS: Geographic Information Systems A short introduction

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GIS: Geographic Information Systems

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Outline

● The Center for Digital Scholarship

● What is GIS?

● Data types

● GIS software and analysis

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Center for Digital Scholarship

• Center services: • Text Analysis • Research design • Data management • Statistic analysis

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What is GIS ?

● In short: “computerized mapping software” ● Formal definition

A Geographic Information System (GIS) is a

computerized database management system for

capture, storage, retrieval, manipulation, analysis

and display of spatial (i.e. locationally defined)

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Layers

● A GIS is composed of

layers of spatial information

● Can be different types

of data ● Everything is referenced to a coordinate system ● e.g. latitude / longitude

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GIS digitally models the real world using:

Three types of geometry -Points

-Lines -Areas

Cells in an image

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Raster Data

– Based on pixel

Vector Data

– Based on discrete points

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● The fundamental unit of a

raster image is the pixel

● This is the same as a digital

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10 m

10 m

Spatial Resolution

The length, in real world measurements, of each side of a square pixel

100 m2

10 m

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Raster Data Model

Raster Advantages

• Continuous Coverage • Detail beyond human

perception

• Easily manipulated

Raster Disadvantages • Fixed resolution

• Large file size

• Difficult to edit individual pixels

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Digital Elevation Model (DEM)

 Type of raster where the pixel value

corresponds to elevation

 Used for analyzing slope, waterflow, visibility,

etc.

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Raster Data

– Based on pixel

Vector Data

– Based on discrete points

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Vectors

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Vector vs. Raster

Vector Advantages

• Economical in space

• Good for discrete features • More flexible with regard

to scale

Vector Disadvantages • More schematized

version of reality • Poorly suited for

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Point Vectors: Field Observations

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Polyline Vectors: Rivers & Ancient Roads

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Polygon Vectors: Agricultural Fields

Polygon Vectors: Ancient fields and city

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Each feature is made up of discrete points

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Each feature is made up of discrete points

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Attribute Data

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Building a GIS map

Individual data layers combine with ways of symbolizing data, charts and figures, editing rules and other tools to form a full GIS map

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Not just pretty maps

• Google Maps and similar software are a type of simple GIS

• Full GIS packages usually have additional editing and analytical tools

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There is very little in the GIS toolkit that cannot be done by traditional means, but it might be computationally

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● GIS adds “space” to research dimensions

● Geographical significance & patterning

– Does location make any difference?

● Real estate, new business locations

– Are there any patterns?

● Migration patterns? How did the disease spread?

● Geographical correlations and relationships

– Are A and B in this location related?

● Crime rate and average income

● Prediction and predictive modeling

– How many people will be affected by something? – Where are we likely to find something?

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Why is GIS important?

Government

80% of local government activities estimated to be geographically

based

• plots, zoning, public works (streets, water supply, sewers), garbage collection, land ownership and valuation, public safety (fire and police)

• natural resource management • highways and transportation

Businesses

• retail site selection & customer analysis

• logistics: vehicle tracking & routing • natural resource exploration

• civil engineering and construction

Military and defense

• Battlefield management

• Satellite imagery interpretation

Research:

• Hard Sciences: Geography, geology, botany, epidemiology • Social Sciences: Anthropology,

sociology, economics, political science

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Example: Patterns

● Socio-economic

– 2000 Census data

– Unit – Census Tract

– Over the community area boundaries

– % families below poverty

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GIS Ex: Patterns – historical/trend

● Trend

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Example: Relationship

• Association

• Demography x Libraries • Are there enough libraries

to serve local residents?

Population density and locations of the Chicago Public Libraries

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Example: Associations

Crime hotspots % families below poverty level

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200 meter rise

Areas impacted

by sea-level rise

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Geographers have even analyzed the distribution of generic names for soft drinks by US county

Same analysis, but done via geotagged tweets

mentioning one of the key words

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Prediction of likely right whale locations off of Cape Cod

Models of plague activity in California ground squirrels

Used to identify potential plague risk areas based on future climate scenarios

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Input Data 1. Soils

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Input Data 2. Slope

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Input Data 3: Vegetation Density (NDVI)

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Complex Calculation: Erosion Risk

Erosion risk model

Use GIS tools to weight each factor and create a single layer representing erosion risk

30 %: Slope

20 %: Vegetation 50 %: Soils

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Final map: Erosion risk is ranked from 1 – 10

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Digital Elevation Model (DEM)

 Type of raster where the pixel value

corresponds to elevation

 Used for analyzing slope, waterflow, visibility,

etc.

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GIS

Software

GRASS: Open source GIS

Quantum GIS: Open source GIS

ArcInfo GIS:

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2d Visualization

ArcMap

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3d Visualization

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GIS resources in the library

• Center for Digital Scholarship

• Bank of 8 computers with extensive GIS software • ESRI ArcGIS

• DIVA-GIS

• GRASS

• Quantum GIS

• Google Earth Professional

• 42” sheet-feed map scanner

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GIS resources in the library

• Staff

Matthew Sisk (CDS): General GIS questions, Data

acquisition and management, Satellite imagery analysis

Milan Budhathoki (CRC): Industry GIS, Vector

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