Environmental Data Types

Spatiotemporal Analysis

Discrete Objects or Entities

• Objects with well-defined boundaries• Points, lines, polygons and areas• Objects or entities have attributes• Can be mobile• Biological organisms

– Animals, trees

• Human-made objects– Vehicles, houses, fire hydrants

• Monitoring/Sensor Networks

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 Earth’s surface– Any field can have slope, gradient, peaks, pits

• Grids

• Soil properties, e.g. pH, soil moisture• Population density

– But at fine enough scale the concept breaks down• Identity of land owner

– A single value of a nominal property at any point• Name of county or state or nation• Atmospheric temperature, pressure

Vector vs. Raster

Vector – Advantages and Disadvantages

• Advantages– Good representation of reality– Relatively compact data structure– Accurate graphics

• Disadvantages– Complex data structures– Some spatial analysis is difficult or impossible to perform

Raster – Advantages and Disadvantages

• Advantages– Simple data structure– Uniform size and shape– Computationally cheaper to process and store

• Disadvantages– Large amount of data– Less visually pleasing (“blocky”)– May lose information due to generalization– Projection transformation is difficult– Different scales between grids can make comparison difficult

Landcover Raster Grid

Legend

Mixed coniferDouglas fir

Oak savannahGrassland (1-5)

(6-10)

(11-15)

(16-20)

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Raster = Grid

columns

row

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The bounding box defines the geographic extent of the grid in terms of its coordinates

Abbreviation for

PICTURE ELEMENT,

which is the smallest

unit in an image. In

raster based GIS

systems, attribute

information can be

assigned to each pixel.

Pixel

Matrix of Equal-Area Cells

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Grid File Format (ASCII)

ncols 6 nrows 6 xllcorner 210yllcorner 370cellsize 20 nodata_value 0 5, 6, 7, 8, 10, 135, 7, 8, 10, 12, 134, 5, 8, 12, 15, 153, 4, 5, 13, 15, 163, 5, 11, 14, 15, 172, 4, 5, 16, 16, 17

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Table Format

X Y Value

220 380 2

220 400 3

220 420 3

220 440 4

220 460 5

220 480 5

240 380 4

240 400 5

240 420 4

240 440 5

240 460 7

240 480 6

Triangulated Irregular Network (TIN)

In a TIN, the world is represented as a network of linked triangles drawn between irregularly spaced points. TINs are an efficient way to store and analyze surfaces. Heterogeneous surfaces that vary sharply in some areas and less in others can be modeled more accurately, in a given volume of data, with a triangulated surfaces than with a raster because many points can be placed where the surface is highly variable, and fewer points can be placed where the surface is less variable.

Contoured Plots

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Also known as an Isopleth Plot

Map Scale

• Map scale is based on the representative fraction, the ratio of a distance on the map to the same distance on the ground.

• Most maps used in GIS fall between 1:1 million and 1:1000.

• A GIS is scaleless because maps can be enlarged and reduced and plotted at many scales other than that of the original data.

• To meaningfully compare maps in a GIS, both maps MUST be at the same scale

Scale of a baseball earth

• Baseball circumference = 226 mm• Earth circumference approx 40

million meters• Scale is 1:177 million

Population Density

County Level Census Tract Level

Resolution25 meter 5 meter

1 meter

Resolution1 meter 5 meter

25 meter

Dimensions

0-dimensionalpoints and nodes

1-dimensional lines

2-dimensional (x,y)areas, polygons

3-dimensional (x, y, z)volumes

4-dimensional (x, y, z, t)3-D and time

2.5 Dimensions

Types of Attributes

• Nominal – Simply identifies or labels an entity so that it can be distinguished from another. e.g. sensor ID, building name (Lopata House vs. Lopata Hall)

– Cannot be manipulated using mathematical operations. However, frequency distributions are meaningful.

• Ordinal – Values based on an order or ranking, e.g. agricultural potential classes

– Cannot be manipulated using mathematical operations. However, frequency distributions are meaningful.

• Interval – Differences between entities are defined using fixed equal units, e.g. Celsius temperature

– Can be manipulated using addition and subtraction

• Ratio - Differences between entities can be defined using ratios, e.g. distance

– Can be manipulated using multiplication and division

• Cyclic - differences between entities depend on direction, e.g. wind direction

A common approach to classifying attributes is based on their level of measurement

Environmental Sensor Data Types

• In situ– Monitor or sensor makes measurements in the media being

measuredAir pollution or water quality networksMeteorological networksField observations

• Remote sensing – Monitor or sensor makes measurements at a distance from the

parameter being measureddoppler radaraircraft imagery (orthophotos)satellite sensors

Thematic Data

Commonly referred to as ‘Base layers’

RoadsRiversPolitical BoundariesElevation (Topography)Land CoverLand Use

Principles of GIS

GISTraditional definition is that GIS is a set of computer tools for accessing, processing, visualizing, analyzing, interpreting, and presenting spatial data.

‘GIS’ is Geographical Information System OR IS IT

Geographical Information Science?

GISystems: Emphasis on technology and toolsGIScience: Fundamental issues raised by the use of GIS, such as

Spatial analysisMap projectionsAccuracyScientific visualization

Implementation and application of GIS covers a wide spectrum:

Simple mapsOverlaying multiple map “layers”Conducting proximity or cluster analysis based on distanceComparing data sets (simple spatial statistics)Complex statistical analysis

Views to a GIS

Map view:

Focus on cartographic (mapping) aspects of GIS

Thematic GIS layers

Input map => Output map

Database view:

Focus on database management system

Simple queries to retrieve and overlay data

Spatial analysis view:

Focuses on analysis and modelling

Views GIS more as information science

Organizational view:

Focuses on decision support systems

An approach to managing an organization’s data, information, and knowledge

GIS as Toolbox

"a powerful set of tools for collecting, storing, retrieving at will, transforming and displaying spatial data from the real world for a

particular set of purposes" (Burrough and McDonnell, 1998)

"automated systems for the capture, storage, retrieval, analysis, and

display of spatial data" (Clarke, 1995)

“an information technology which stores, analyses, and displays both spatial and non-spatial data” (Parker 1988)

GIS as Database

“a database system in which most of the data are spatially indexed, and upon which a set of procedures operated in order to answer queries about spatial entities in the database” (Smith et al., 1987)

"A geographic information system 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)

GIS as Spatial Analysis

"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)

“The true potenital value of Geographical Information Systems lies in their ability to analyse spatial data using the techniques of spatial

analysis" (Goodchild, 1988)

GIS as Organization

“ an institutional entity, reflecting an organizational structure that integrates technology with a database, expertise and continuing

financial support over time” (Carter, 1989)

“organized activity by which people measure and represent geographic phenomena, and then transform these representations into other forms while interacting with social structures.” (Chrisman, 1999)

“ a decision support system involving the integration of spatially

referenced data in a problem-solving environment” (Cowen, 1988)

GIS as Science

Geographic Information Science is research both on and with GIS.

"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)

Components of a GIS

• Organized collection of– Hardware– Software– Network– Data– People– Procedures

PeopleSoftware

Data

Procedures

Hardware

Network

“GIS should be viewed as a process rather than as merely software or hardware.” (Malczewski, 1999)

A Brief History of GIS

• GIS’s origins lie in thematic cartography • Many planners used the method of map overlay

using manual techniques • Manual map overlay as a method was first described

comprehensively by Jacqueline Tyrwhitt in a 1950 planning textbook

A Brief History of GIS

• The 1960s saw many new forms of geographic data and mapping software

• Computer cartography developed the first basic GIS concepts during the late 1950s and 1960s

• Linked software modules, rather than stand-alone programs, preceded GISs

• The Harvard University ODYSSEY system was influential due to its topological arc-node (vector) data structure

User Interface Applications

Geographic Tools

Data AccessSpatial

ReferenceVector

DataManager

Raster

Output

Editing

Analysis

CustomizationDisplay

Translation

Functionality Architecture

Map Overlay

Figure 1.3 Map overlay as presented in Design with Nature by Ian McHarg. Each transparent layer map“blacked out” areas excluded as unsuitable locations.

SOILS

PARKS

URBAN

SOLUTION MASK

FOREST

Definition 4: GIS is a multi-billion dollar business.

“The growth of GIS has been a marketing phenomenon of amazing breadth and depth and will remain so for many years to come. Clearly, GIS will integrate its way into our everyday life to such an extent that it will soon be impossible to imagine how we functioned before”