Introduction to GIS

• What is GIS?– Benefits of GIS– What can you do with GIS– The Geographic Approach

• Who uses GIS?• Careers in GIS

http://www.esri.com/

Uses of GISToday, biologists use collar transmitters and satellite receivers to track the migration routes of caribou and polar bears to help design programs to protect the animals. In a GIS, the migration routes were indicated by different colors for each month for 21 months. Researchers then used the GIS to superimpose the migration routes on maps of oil development plans to determine the potential for interference with the animals (USGS).

http://egsc.usgs.gov/isb/pubs/gis_poster/

What is GIS?• Geographic Information (GI)

• Data – raw recording for measurements used to create information – raw material for Geographic Information– When used by a GIS it becomes GI– One person’s data is another person’s information

• Maps – tools for storing geographic info and for analysis and display– Cartography– Abstractions focused on selection of things– Purpose

What is GIS?• Information Technology

• Geographic Information Systems (GIS)– managing information– spatial (or geographic) info– Planning

• What is GIS? - a set of tools (a computer system) for collecting, storing, analyzing, and displaying geographic information (GI) for a particular set of purposes– Practitioners also define a GIS as including the procedures,

operating personnel, and spatial data that go into the system

What is GIS?• Steps:– identify issues, data– gather data (maps, statistical data, remote sensing,

GPS)– digitize or download digitized data– overlay– analysis of output

• Questions usually asked when using GIS?– location of features– geographical patterns– changes that have occurred – spatial implications

Data Integration

Data integration is the linking of information in different forms through a GIS.

Data Overlay – “Layers”

What is GIS?• 3 components: – computer system - hardware, software, and peripherals– spatial data - geog. info – management and analysis of data

• Functions GIS perform:– Data input – graphical, attribute– Storage– Management – store, organize, retrieve data– Transformation – change projection of map layer, correct

errors from digitize, convert raster data to vector data– Analysis – query data, predictions

• layers: roads, cities, rivers, topography• one entity per layer (point, line, polygon)

– Output – maps (layouts), tables, graphs (charts)

Representation and Communication

• Geographic Rep. = Making observations of the world and put into things and events – result in a model– Scale

• Cartographic Comm. = symbolizing the representation

• Things and Events– static change– objects processes – ice melt, disease, soil erosion– Features– p. 8 p. 10

Geographic Information• Features - spatial/graphical entities• 3 types of features:– Points - x,y coordinates

• Cities, places– Lines - string of x,y coordinates joined together in

order and connected with straight lines• an ordered set of points• roads, railways, rivers, boundaries• network = extension of line features

– Polygons – areas• closed set of lines• fields, metropolitan areas, buildings, forest, lake, park,

industrial area, mountains• surface = 3 dimensional area

– elevation

Geographic Information

• Attributes - non-spatial data that describe what the features represent – the properties – characteristics and qualities of things and events – info about map features– features displayed in map are based on attributes– linked to features and associated with point, – line, and area entities by way of themes

• Themes – units that link features with their attributes

• displayed as layers in GIS• features with a set of common attributes• stored as tables• select attributes to find features (highlight)

Geographic & Cartographic Representation• Types of Maps

– Thematic – specific topics • Weather forecast, climate, biomes, election results, soil types, income

distribution, spread of disease– Topographic – physical features on the landscape based on variation

in elevation– Cadastral – property divisions

• Geographic representation – selection of observations, measurements, and choices about their

coding as attributes– What aspects people choose about the world and how they choose to

show them on a map or as geog info

• Cartographic representation – selection of graphical elements and abstraction of geog info to

communicate for a purpose– How they then choose the symbols in order to communicate the

chosen geographic information effectively

Data Modeling

Points with pH values of oil Contour map made from soil pH values

Geographic & Cartographic Representation• 4 types of measurement:– nominal – to establish identity

• qualitative measurements• good for text (name, type, state)

– ordinal – to establish order• quantitative measurements - order but no beginning• value (small, medium, large)

– interval – to establish variation • quantitative measurements with defined beginning point• (temperature, height, distance)

– ratio – difference between numbers significant• quantitative measurements that provide a relationship

between 2 properties • Usually has mathematical calculations• Time to cover a distance

– p. 40

Geographic & Cartographic Representation

• 2 models, or structures, for representation of GI:– These involve space, attributes, and time (fixed)– vector – areal extent of the attribute

• measure space (area)• attribute is fixed• points, lines, areas• ex. – networks (rivers, roads, etc.), boundaries

– raster – presence of the attribute • measure the attribute • cells (area) or pixels (dots)• ex. - remotely sensed imagery

Data Structures

Example of the structure of a raster file. Example of the structure of a vector data file.

Raster format Vector format

Projection

• 4 choices in creating Geog Info:– Projection, Scale, Data, Symbols

• Projection – transform the spherical onto a flat, 2-dimensional surface – flattening

• 3 models of the earth:– spheroid – OK for very large areas– ellipsoid – oblate spheroid – accurate enough for

smaller areas– geoid – most accurate representation of earth’s

actual surface – constantly changing shape

Geoid Earth

Projection

Projection

• Types of projections: – Conformal/conic

• Mercator– Transverse Mercator and Oblique Mercator

– Equivalent/equal area • Sinusoidal• Lambert Conformal Conic

– Azimuthal • Stereographic

– Equidistant/cylindrical – Compromise

• Robinson• Fuller

Projection• Conformal/conic– Preserve angular relationships from one point

(angles/shapes only)– Not areas – Areas of continents or countries can change – Shapes conform to actual shapes on earth – Mercator

• Transverse Mercator and Oblique Mercator• Lines of a constant direction are straight lines• Good for navigation at sea • Preserves angles = shapes • Great circle distance – shortest distance on a sphere• Size distortion

Projection• Equivalent/equal area – Preserve area by a constant scaling factor– Not shapes – Shapes of continents or countries can change– Areas conform to actual areas on earth– Sinusoidal– Preserves areas– Distorts angles and shapes – Used to show distribution patterns – Lambert Conformal Conic – Preserves only angles – Used for mapping continents or large countries like USA

(E-W orientation)

Projection• Azimuthal – Preserve directions – only from center of map – Stereographic – Preserves direction – Shows great circle routes as straight lines– Used to show airplane navigation routes

• Equidistant/cylindrical • preserves distance • Compromise – Robinson– Preserves no properties but is attractive– Fuller

ProjectionTypes

Projection Conflicts

An elevation image classified from a satellite image of Minnesota exists in a different scale and projection than the lines on the digital file of the State and province boundaries.

The elevation image has been reprojected to match the projection and scale of the State and province boundaries.

Projection Conflicts

Locational and Coordinate Systems• 4 fundamental concepts: – Earth always changing shape– All projection make compromises– Distortions always occur – Never combine geographic info from different

projections

• Locational systems – Not associated with projection or model of earth – Locally defined coordinate system– Public Land Survey

Townships and Range System

Locational and Coordinate Systems

• Rectangular Coordinate systems– Associated with projection or model of earth’s size

and shape– Latitude and Longitude– Metes-and-Bounds– State-Plane Coordinate System– Universal Transverse Mercator (UTM)– Polar coordinate systems– Spherical coordinate systems

Latitude and Longitude

UTM System

Scale

• Scale – ratio of distance on the map or screen to the corresponding distance on the ground– represented as ratio, verbal, or graphic– large scale = greater accuracy and detail– smaller area represented on map– small scale = less accuracy and detail– larger area represented on map

Data• Database = collection of data stored in a structured

format using a computer (Table) – Field – division of data into separate parts of each data

item• Column for each category of info – attributes• Attribute – particular entry in a field (South Carolina in the field

“State”– Record

• Row for each feature in the layer – Features on a GIS map are linked to the info in their

attribute table

• Relational database – as opposed to flat-file database– Stores data in separate files called “tables”

• New features can be created from areas of overlap– New layer created

Types of Data– Analogue Data

• tabular, map, aerial photos (digitizing, scanning)– Digital Data

• tabular, map, satellite imagery• transferring digital files to shapefile (SHP) or dBASE file (DBF)• graphical data from jpeg

– integer data• whole #s

– Floating-point• #s with decimals

– Character string• text

– Date and time, time interval• Events or when things were recorded

– Single large objects – binary large objects (BLOBs)• Images

Data Sources• Surveying, GPS, digitization • Surveying/geodesy – systematic collection of

positional and attribute information• GPS – system of satellites launched and maintained

by the U.S. Dept. of Defense– Over 50 satellites launched– Galileo – E.U. system with over 30 satellites– Radio signals used to calculate time difference between

receiver and satellite (binary signal)– GPS receiver – computer chip

• Digitization – Maps (U.S.G.S.)– Tablet digitizing– Heads-up digitizing – georeference to coordinate system – Scanning – faster

Integration of Data Sources

Data integration is the linking of information in different forms through a GIS.

Remote sensing• Measuring object from a distance using reflected or

emitted electromagnetic radiation• Electromagnetic radiation (EMR)– Incoming, reflected, emitted

• Electromagnetic spectrum – Radio, microwave, infrared, visible, ultraviolet, X-ray,

gamma ray– Spectral bands – ranges

• Resolution– Spatial resolution – size of unit recognized by sensor– Temporal resolution – frequency of readings taken by

satellite• Spectral resolution – range of wavelengths a sensor

can record

Electromagnetic Spectrum (EMS)

Remote Sensing• Types of sensors:– (Aerial) Photography– Infrared (photography and imagery) – Radar – radio waves – Laser (LiDAR) – Light Detection and Ranging– Satellite imagery

• collection of pixels (raster cells)• (smaller pixel = higher spatial resolution)• Multispectral

– Multiple bands – Landsat– SPOT

• Hyperspectral– Hyperion

Satellite Imagery

Landsat Thematic Mapper image of San Mateo County, Calif.

GI Representation• Position-based thing or event represented as a

discrete record of location and properties – Most common storage techniques are raster and

vector– Vector GI stored most often as georelational model

format• Relies on topology – geometric relationships of between

spatial entities • 3 components of georelational model:

– Table with a list of polygons (areas)– List of chains (lines or arcs)– Table of nodes

– Raster GI – encoding techniques including quad-tree hierarchy

GI Representation• Network-based

– things and events represented are recorded using an ordered arrangement of connecting points (nodes), lines, and areas

– Nodes and links correspond to nodes and chains in vector position-based representation

– Topological info important• Field-based

– used to represent nondiscrete things and events– include anything that can be observed or sensed but does not

have clearly identifiable limits• ozone, soil pH, CO2

– Environmental modeling– Uses raster data structures– Triangular irregular network (TIN)

• format for the representation of fields that relies on a network of lines connecting points with values

• Used for visualization of elevation data

Topology

London Underground

GI Representation

• 2 most fundamental GIS operations:– Buffer transformations • Transform position-based GI into other types of

position-based GI or into fields

– Overlay transformations (most important)• Transform two or more position-based GI data sets into

one• Combines the geometry (points, lines, polygons) of 2 or

more data sets based on a common coordinate system

Data Output• Geographic representation – abstracts things and events from the

world• Cartographic representation – creates visual techniques and forms

for geographic representation– Maps and visualization

• Main issues:– Scale– Generalization – abstraction of features to reduce complexity in maps– Classification – used for quantitative data (ordinal, interval, and ratio),

nominal only as individual categories• Equal interval – divide in to equal parts (between min. and max. value)

– Things with implicit order• Quantile – each class has approx. same number of features• Natural break – maximizes differences and keeps similar clusters together • Standard deviation – shows how much a geographic unit’s property varies

from the mean– Average value

– Symbolization– Color (Hue)

Scale and GeneralizationDigital revision of 1:100,000-scale digital line graph data to produce a 1:500,000-scale New Jersey State base map. Paneling and generalization are shown in three stages from 1:100,000 scale to 1:250,000 scale to 1:500,000 scale.

These digital maps of Bergen County, N.J. are all at the scale of 1:500,00. The information content of the maps has been reduced through the process of generalization in two stages, from 1:100,000 scale on the left to 1:250,000 in the center, then from 1:250,000 to 1:500,00 scale on the right.

Data Output• Important map elements:

– Scale, Legend, Title, Author, Orientation, Date

• Cartographic presentation types:– Topographic maps

• vary from 1:10,000 to 1:100,000– Cadastral maps

• show land ownership – Thematic maps

• demographic issues (birthrates, income groups, etc.), environmental issues (climate, soils, etc.)

– Chloropleth maps– Dasymetric maps– Charts– Cartograms

• show quantitative difference by altering the size of the geographic units according to the relative proportion of the unit’s property

– Dot-density maps • show the quantity of a property by placing a dot in a geographic unit for each

incident of the property

Colonial Possessions, 1914

Thematic Maps

Thematic Maps – Church vs. Beer

Figure 1.24

Chloropleth Maps

World Population Cartogram

This cartogram displays countries by the size of their population rather than their land area. (Only countries with 50 million or more people are named.)

Dot Density Maps

Data Output

Examples of finished maps that can be generated using a GIS, showing landforms and geology (left) and human-built and physical features (right).