Geog 255 Part 1

Front 1

Geographic information

Back 1

Info about where something is or what is at a certain location

It can be detailed, and coarse

- need info about location/time/ attributes

Example: a forest where a few spotted owls remain

- WHERE spotted owls are is geographic info or location

- WHAT Trees grow in the areas inhabited by the owls is also geographic info

Front 2

What is GIS?

Back 2

Geographic information systems

A tool

A special purpose database in which a very common spatial coordinate system is the primary means of reference

Covers measurement, characterization, data representation, visualization, and analysis

Front 3

What does a comprehensive GIS require?

Back 3

1. Data input from maps, aerial photos, satellites, survey, etc.

2. Data storage, retrieval, query system

3. Data transformation, analysis, modeling, including spatial analysis

4. Data reporting, such as maps and reports and plans

Front 4

What is GISci?

Back 4

GISc/GIScience

The theories and ideas

Front 5

Themes raised by GIS

Back 5

1. All info in GIS is linked to a spatial reference.

- uses geo-references as the primary means of storing and accessing info

2. GIS integrates technology

3. GIS should be viewed as a process rather than merely a software

Front 6

Chrisman 1997 definition of GIS

Back 6

The organized activity by which people...

Measure... aspects of geographic phenomena and processes

Represent... the measurements, usually in the form of a computer database to emphasize spatial themes, entities, and relationships

Operate... upon these representation to produce more measurements and to discover new relationships by integrating disparate sources

Transform... these representations to confirm to other frameworks of entities and relationships

Front 7

What are we interested in?

Back 7

The geographic question, at all times. GIS provides tools to expedite the spatial analytical process

Front 8

Phenomena

Back 8

Change in space and time

Can be viewed (& represented) across many scales and resolutions. The way we record and represent them influences the way they are perceived and understood

Front 9

GISystems

Back 9

Refers to a collection of practices, software, and hardware with the ability to collect, store, analyze, and print information about the earth's surface (or any other scale of geographic data)

Front 10

GIS vs GIScience

Back 10

GIS: a mix of hardware and software used to run a spatial analysis and mapping programs

GISc/GISci/GIScience: theoretical and conceptual basis for procedures incorporated in GIS software.

Front 11

Mapping process

Back 11

A process of communication, concepts/ facts transmitted through maps

Data collection

Map construction

Map use

Map reading

Map analysis

Map interpretation

Front 12

Promises of GIS

Back 12

1. Ability to integrate large quantities of information

2. Powerful repertoire of analytical tools

3. Maps layers can be arrayed to display different information

4. Ability to separate information into layers and then combine it with other layers of information

Front 13

Before leaping into a GIS project...

Back 13

1. What it's your objective

2. What are you trying to determine

3. So what variables would you need

4. What relationships would you be trying to show

Front 14

Transect

Back 14

A linear path from a to b.

Looking at how variables change across that path.

Front 15

Entity definition

Back 15

Bare geometry as a way to classify things in reality. Points, lines, areas, volumes. Sometimes also called entity definition.

The way we conceptualize objects in the real world as one or more types of spatial entities (points, lines, areas)

Examples:

- bus point = point like

- street network = line like

- footprint of the auditorium = area like

Front 16

Vector GIS

Back 16

Represents points, lines, and area like features through connections of points and lines

Front 17

Discrete phenomena

Back 17

Relatively easy to identify the start/end or where they exist/ do not exist.

> can define by capturing the coordinates of each corner

> each point/node must be connected - vector representation of the footprint of this feature

> the feature only exists in one single point in space

Front 18

Continuous phenomena

Back 18

Exist, potentially everywhere in varying degrees

- elevation, temperature, pressure...

- no fixed borders

- must assign discrete variables to the data in order to store the data spatially (discretization)

Front 19

Discretization

Back 19

To sample reality by assigning discrete values to continuous phenomena in order to create a representation of that phenomena.

4 methods.

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Discretization method 1

Back 20

Taking measurements at sample points (weather stations, traffic counters, intersections)

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Discretization method 2

Back 21

By taking transects or cross-sections at intervals. Then interpolate between sample sites - geological sampling

Front 22

Discretization method 3

Back 22

Divide the area into patches/zones, and assuming the variables are constant within each zone.

- Soil mapping

- Within the zones, the variable is homogeneous

- the principle behind enumeration for the census tracts

Front 23

Discretization method 4

Back 23

Drawing contours, elevation in topographic maps

Front 24

Problems with discretization

Back 24

- each method creates discrete objects (lines, points, areas)

- each method is approximate, capturing only part of the real variation

What data is missed/lost through this process?

What is sampled/represented?

Has a transformation occurred?

Usually loss of data

Front 25

Binary logic

Back 25

Yes/no, black/white

Front 26

Fuzzy logic

Back 26

More than just two states of an object.

Where does a forest begin? Where the density surpasses a defined threshold.

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Concrete frames of reference

Back 27

Or absolute.

External frame of reference, relationships- distance

Front 28

Abstract frames of reference

Back 28

How do we locate ourselves and other things

Places and place names (here and there)

Front 29

Geographical grid

Back 29

Plane grid- Most convenient, but least accurate

Spherical coordinate system with latitudes and longitudes used for determining the locations of surface features.

Front 30

Parallels

Back 30

Latitude.

East-west lines parallel to the equator.

Are constantly parallel.

Meridians and parallels always intersect at right angles.

Front 31

Meridians

Back 31

Longitude

North-south lines connecting the poles.

Meridians converge at the poles.

Meridians and parallels always intersect at right angles.

Front 32

Latitude

Back 32

Parallels.

Is an angle from the equator (N, S).

Notation: degrees, minutes, seconds, N, S

Front 33

Longitude

Back 33

Meridians

The angle around the earth.

Measured from an arbitrary zero (prime meridian, Greenwich).

Notation: degrees, minutes, seconds (E / W)

Front 34

What is map protection?

Back 34

Transformation of the spherical surface into a plane surface. All meridians, parallels, human, and physical features are transformed.

Front 35

Significance of map projections

Back 35

1. Distortion is always introduced

2. Distortion is inevitable but you can choose different types

3. Goal= select a MP with distortion that does not interfere with the purpose of your geographic inquiry

4. A poorly chosen map projection can distort your thematic data

Front 36

Developable surface

Back 36

A developable surface is a simple geographic form capable of being flattened without stretching. The point of direct contact between this surface and the generating globe has no distortion

What kinds of flattenable surface are spheres projected onto?

Plane, cylinder, cone = azimuthal, cylindrical, conic projections

Front 37

Azimuthal (planar) Map Projections

Back 37

Surfaces projected onto a planar surface

1. Tangent at a point on the sphere (simple form): standard point

2. Pass through a sphere (secant form): standard line

Front 38

Tangency in Azimuthal MP

Back 38

Tangency: varies the projection

- polar aspect: tangency at a pole

- oblique aspect: tangency at mid-latitude

- equatorial aspect: tangency at equator

Front 39

Distortions in Azimuthal MP

Back 39

Increase from a standard point or line

- increase outward in concentric bands

- conformal Azimuthal projections: area exaggeration increases outward

- equal area Azimuthal projections: shape distortion increases outward

- can be varied to preserve area, angle, distance, direction

Front 40

Cylindrical Map Projections

Back 40

Projection onto a cylinder

- tangent at 1 or more lines: standard lines

- equator is the most standard line

- tangency can be varied

- distortions increase away from the lines or tangency

Mercator, traverse mercator, Robinson

Front 41

Conic Map Projections

Back 41

Projection onto a cone.

- tangent along one or more standard lines

- distortion increases away from line of tangency

- albers projection and patterns of distortion

- amulet projection and patterns of distortion

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Tissot's Indicatrix

Back 42

A way to compare relative distortion of different projections

1. Perfect circles of equal size on globe

2. Reveals patterns of distortion on projected maps

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Conformal map

Back 43

Maps that preserve shape

Front 44

Equivalent maps

Back 44

Maps that preserve area

Front 45

Equidistant maps

Back 45

Maps that preserve distance.

Front 46

Projection

Back 46

The transformation and representation of three dimensional space as two dimensional surface

Front 47

Coordinate system

Back 47

A reference system for measurements defined by the projection

Front 48

Geographic coordinate system

Back 48

Measures locations in degrees (lat, long)

Major parameter is it's datum.

Front 49

Projected coordinate system

Back 49

Uses a projection to transform the latitude and longitude to X and Y coordinates. Based on a geographic coordinate system.

Makes the linear measurements more accurate.

Front 50

Geodesy

Back 50

The study of the shape of the earth

Front 51

Ellipsoid

Back 51

A mathematical approximation as a representation of earth.

Attempt to find a reasonable fit to the geometry in question

Front 52

Projected data

Back 52

Data explicitly projected in a projected coordinate system

Front 53

Unprojected data

Back 53

Data in a geographic coordinate system and projected in its raw form.

Not projected to a plane, cylinder or cone. Data is in lat/long.

Front 54

Analogue data sources

Back 54

Paper, nondigital. Illustrations, photographs, questionnaires, etc.

Front 55

Digital data sources

Back 55

Nonpaper data, digital, stored online. GPS data, excel spreadsheets, digital data sets...

Front 56

Primary data

Back 56

Data directly sampled/ gathered

Front 57

Secondary data

Back 57

Data purchased/ procured from original source of sampling

Front 58

Value of quantitative data

Back 58

Repeatable

Front 59

GPS - global positioning system

Back 59

A system of: earth orbiting satellites transmitting precisely timed signals, ground control stations, mobile receivers for consumers.

- provide direct measurement of position on the earth's surface

- location expressed in long/lat

Front 60

Accuracy

Back 60

Represents how close to a measurement comes to its true value

Front 61

Precision

Back 61

How close a series of measurements are to eachother

Hire reproduceable measurements are

Front 62

Spatial data

Back 62

Where things are

Front 63

Attribute data

Back 63

What things are.

Ex: material, weight, height, elevation

Front 64

Geoid

Back 64

Model of shape if the earth based on msl(mean sea level). Trying to average out the highs and lows of the surface geometry of the whole planet

Front 65

Datum point

Back 65

A reference point from which measurements are made from. Serves to provide known locations to begin surveys and create maps.

Front 66

Horizontal datum

Back 66

Used for describing a point on the earth's surface, in latitude and longitude, or another coordinate system

Front 67

Vertical datums

Back 67

Used to measure elevations or underwater depths

Front 68

Geodetic datums

Back 68

Define the reference for our characterization of the size and shape of the earth and the origin and orientation of the coordinate systems used to map the earth

Front 69

Datums: considerations and implications

Back 69

1. Referencing geodetic coordinates to the wrong datum = position errors

2. Different nations and agencies use different datums

3. Requires careful datum selection and careful conversion between coordinates in different datums

Front 70

Vector data model

Back 70

Geographic entities stored as nodes, line segments, and polygons.

Basic units = points (nodes), lines (arcs), and polygons

Efficient- does not represent empty space

Unique for geographic phenomena edith complex geometry. Stores typology.

- uses discrete line segments or points to identify

- discrete objects (boundaries, streams, cities) are formed by connecting line segments

- vector objects do not necessarily fill space, empty space is described within boundaries of the polygon

- tells where everything occurs, gives a location to every object

Front 71

Raster data model

Back 71

An abstraction of the real world where spatial data is expressed as a matrix of cells or pixels, with spatial position implicit in the ordering of the pixels.

Data divided into discrete units. Used for algorithmic analysis of continuous data.

Each cell contained location coordinates + attribute value.

Stores empty features in cells.

Often used for algorithmic analysis of continuous spatial data.

- tells what occurs everywhere, at each place on the area

Front 72

Reference map

Back 72

Serve as base maps.

General purpose emphasis on geometric properties (distance, direction, area).

Some not specifically interpreted (air photographs). Some are highly symbolic (topographic, nautical charts).

Front 73

Thematic maps

Back 73

Special purpose, emphasis on a single theme not position extreme form of thematic maps.

Cartograms- distort geometry on purpose

Mapping crime/ particular forms of crime

Front 74

Digitization

Back 74

Making analogue data sources digital

Front 75

Topography

Back 75

The precise physical location and shape of geographical objects

Front 76

Quantification

Back 76

May be simple or complex.

Simple: the maximum height of a mountain

Complex: coding the characteristics of the forest

Front 77

Data Structure

Back 77

Refer to the way the data is stored in the computer.

Usually compatible with computer architecture.

Front 78

Data Models

Back 78

A reflection on the way that we're imagine geographic space.

Vector and raster

Front 79

3 main database models

Back 79

1. Hierarchical data structures

2. Network systems

3. Relational database structures

Front 80

Topology

Back 80

The logical relationships between the position of those objects.

Stores relationships of one spatial element with respect to another.

Relationships: adjacency/ connectedness/ containment

Front 81

Entity

Back 81

An individual point, line, or area in a GIS database

Front 82

Attribute

Back 82

Data about an entity.

In a vector GIS, stored in a database. In raster GIS the numerical code/ value of each cell represents the attribute present.

Front 83

Feature

Back 83

An object in the real world (to be) encoded in a GIS database.

Front 84

Data layer

Back 84

A data set for the area of interest in a GIS (separate layers for roads, buildings, services, etc.)

Front 85

Image

Back 85

A data layer in a raster array.

Front 86

Cell

Back 86

An individual pixel in a raster image/array

Front 87

Function/operation

Back 87

A data analysis procedure performed by a GIS

Front 88

Algorithm

Back 88

The computer implementation of a sequence of actions designed to solve a problem. (Applying mathematical rules to all cells in a raster array)

Front 89

Euclidean

Back 89

A straight line, point to point distance

Front 90

Perimeters

Back 90

The sum of straight line lengths

Front 91

Areas

Back 91

The sum of areas of simple geometric shapes

Front 92

Attribute queries

Back 92

Questions about the attributes of features. A spatial since the question & answer contains no analysis of spatial component of data. Could be performed by analysis of database.

Front 93

Spatial queries

Back 93

Location added to attribute query... now a spatial query

Front 94

Boolean operations

Back 94

Used to determine inclusion, exclusion, intersection, and union.

To operationalize queries.

Critical part of vector overlay.

Expressions: and, or, not, xor

not, xor

not, xor

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Union: Boolean Overlay

Back 95

The combined area of two queries. The combined area = A.OR.B

Front 96

Intersection: Boolean Overlay

Back 96

The area of overlap of A and B = A.AND.B

Front 97

Clip: Boolean Overlay

Back 97

The area remaining when you trim/crop A using the portion of B that overlaps it. (A.NOT.B)

Front 98

Buffer

Back 98

A construct around a point, line, or area that creates a new area, enclosing the buffed object.

Ex.

- protected zone around lakes

- service zone around bus route

Front 99

Setbacks

Back 99

Like a buffer but constructed on the inside of a boundary. Regulations often made by municipalities.

1703, America, setback minimums for front yards in Williams-burg, VA

Front 100

Vector overlay

Back 100

Requires the production of geometric composites with each new area having the key to source the attribute tables.

Relationships between features: proximity, containment, overlap

Hint 100

Front 101

GIS intersect

Back 101

A process that takes two (or more) feature layers and determines where they spatially intersect. These are the areas where the two features share the same space. Results contain only where the features overlap

Front 102

Dissolve, topical overlay

Back 102

Removes boundaries between polygons or nodes between arcs.

Features with the same attributes are dissolved.

Front 103

Union, topological overlay

Back 103

All input features from both layers remain.

Attribute values are assigned by containment.

Attribute inheritance

Polygon & polygon only

Front 104

Intersect, topological overlay

Back 104

Refer to "GIS intersect"

Only features from overlap area exist in output. Attributes from both layers exist. Order of input and overlay does not matter.

Polygon on polygon, line, or point

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Clip, topological overlay

Back 105

"Cookie cutter"

Only input layer features and attributes exist in output.

Polygon on polygon, line, or point

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Topological overlay types

Back 106

Front 107

Topology during spatial overlay

Back 107

1. Overlay 2 layers of area objects

2. Intersections between boundary lines of the polygons are computed

3. Boundaries are broken at each intersection

4. The intersections become new nodes in a composite typology

5. New polygons are labelled

Front 108

Manhattan (network) distance

Back 108

The distance between two points measured along axes at right angles

Picture- green=euclidean

Front 109

Viewsheds

Back 109

Viewsheds: are the portions of terrain that you can see from a certain vantage point

Front 110

Vector viewsheds

Back 110

Construction of viewsheds relies on ray tracing.

Front 111

Ray tracing

Back 111

A line is drawn from the origin point to all possible points in the coverage. Then the rays are followed, testing for elevation at each recorded intervening point.

As soon as a higher point is found, the viewshed is terminated in that direction.

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Model builder

Back 112

Allows you to explicitly specify the process/ operation(s) you want to perform on data

- graphical interface to process modeling in GIS

- self documenting/exposed

- file-based, stored with map document or stored with geodatabase

- can be shared

- built-ins, VBA, scripted tools (java)

Front 113

Census

Back 113

A (usually complete) enumeration of a population; specifically: a periodic governmental enumeration of population

Front 114

Census tract

Back 114

A geographic region defined for the purpose of taking a census

Front 115

Choropleth mapping

Back 115

Using areal units to map variables. Allows us to attach quantified variables to predefined geographic areas.

Areal units may be:

- administrative areas

- census transects

- municipalities health service regions

Front 116

Cartogram

Back 116

A type of map that shows statistical information on a diagrammatic form

Front 117

Types of raster cell values

Back 117

Depends upon the reality being coded and the GIS

diff systems allow diff classes of values:

- whole numbers (integers)

- real (decimal) values

- alphabetical value

Front 118

Cell values (raster)

Back 118

Many systems only allow integers. Others allow different types, but restrict each separate raster layer to a single kind of value.

Each cell is assumed to have one value. Inaccurate, a boundary may run across the middle of a pixel. In such cases a pixel is given the value of the largest fraction of the cell, or the value of the middle point of the cell.

Front 119

Number substituting for ordinal data

Back 119

Integer values often act as a code number, which point to names in an associated table or legend.

Front 120

Methods for determining which value is assigned to cells

Back 120

1. Values are averages for cells

2. Values are samples at cell centers

3. Values are samples at the grid nodes

Front 121

Resolution

Back 121

Three minimum linear dimension of the smallest unit of geographic space for which data are recorded.

Front 122

Raster resolution

Back 122

Refers to linear dimension of each cell.

Refers to relative density of cells per unit area.

The higher the resolution of a raster, the smaller the cell size and thus, the greater the detail.

Front 123

Spatial resolution vs scale

Back 123

Spatial resolution: the dimension of the cell size representing the area covered on the ground.

- if the area covered by a cell is

5x5 m then the resolution is 5m

The smaller the scale the less detail shown.

Front 124

Advantages of raster

Back 124

- simple data structure

- compatible with remotely sensed or scanned data

- simple spatial analysis procedures

Front 125

Advantages of vector

Back 125

,- requires less disk storage spaces

- topological relationships are readily maintained

- graphical output more closely resembles hand-drawn maps

Front 126

Disadvantages of raster

Back 126

- requires greater storage space

- graphical output may be less pleasing

- projection transformations are more difficult

- more difficult to represent topological relationships

Front 127

Disadvantages of vector

Back 127

- more complex data structure

- not as compatible with remotely sensed data

- software and hardware are often more expensive

- some spatial analysis procedures may be more difficult

- overlaying multiple vector maps is often time consuming

Front 128

Distances in raster

Back 128

Euclidean

Manhattan

Proximity

Front 129

Local operations

Back 129

- produce a new layer from one or more input layers

- the value of each new pixel is defined by the values of the same pixel on the input layer

- neighboring or distant pixels have no effect

- note: arithmetic operations make no sense unless the values have appropriate scales of measurement

Front 130

Recoding or reclassification

Back 130

GIS allows us to make decisions based on likeness

To determine if certain conditions are met. To combine layers.

Useful when the number of unique input values has little variation or when the old layer has different values in each cell (can aggregate them).

May sort the unique values found on the input layer and replace by the rank of the value. To make it easier to see spatial structures and distribution.

Front 131

Reclassification as raster overlay

Back 131

Occurs when the output value depends on two or more input values

Front 132

Local neighbourhood operations

Back 132

Assigning values to a raster cell, by sampling the values of local neighboring cells in the raster array.

The value of a pixel on the new layer is determined by the local neighborhood of the pixel on the old layer.

Not many cells away but a few cells away

One of the most useful is filtering

Front 133

Filtering

Back 133

Operates by moving a window across the entire raster

Frequently used in image processing, sometimes used to compare values in the window with those on the raster layer

Front 134

High pass filters

Back 134

Filters that are used to isolate edges (or water bodies or crop extents) or linear features (mountains).

Edge enhancement (exaggerates local detail)

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Low pass filters

Back 135

Used to smooth out exceptional features.

To eliminate pockets of unusual values. (Eliminate a tiny pocket of low income in the midst of a prosperous area).

Remove or reduce local detail

Front 136

Isotropic distance

Back 136

Calculate the distance from each cell from a cell or the nearest of several cells.

Result is isotropic surface

Front 137

Friction distance

Back 137

Another type of surface based on distance measurements

Distance is weighted

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Impedance distance

Back 138

When there is a barrier between two areas, we also calculate impedance values.

Barriers may be absolute (mountain range) or relative/ partial

Front 139

Variable buffers

Back 139

Created by assuming different impedance values around different portions of the line, point, or area.

Front 140

Seacant vs tangent

Back 140

Front 141

Projected data

Back 141

Data projected in a projected coordinate system

Front 142

Unprojected data

Back 142

Data projected in a geographic coordinate system, in it's raw format