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GIST 7100 - Fundamentals of GIS > Final Exam Review > Flashcards

Final Exam Review Flashcards

1
Q

What are the four components of a network?

A

Links, nodes, stops, and centers

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2
Q

What term is used to describe distance along linear referenced segment?

A

Measure

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3
Q

How are linear referencing and dynamic segmentation related?

A

Can use measures stored in event tables to create dynamic segments along linear references routes

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4
Q

What are the two types of linear referencing events?

A

Point and line

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5
Q

What is geocoding?

A

the process of assigning real world x,y location to a nominal location

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6
Q

Describe the characteristics of discrete georeferencing systems

A

Use nominal descriptors for locations.
Coord sys. for discrete georeferencing systems are linked to a human-defined “structure”

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7
Q

Provide three examples of discrete georeferencing systems.

A

1) Area partitioning schemes- ex postal codes
2) Street Addressing
3) Linear referencing- transportation route measures

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8
Q

What are the two types of geocoding?

A

1) Zone based - ex. the centroid of a boundary,
2) Address Interpolation-> most common

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9
Q

How does the address geocoding process work?

A

The addresses to be geocoded are parsed and compared to an existing street network file. Each address is matched to a specific street segment attributed with address ranges. The position of the address is then interpolated within the range along the segment.

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10
Q

What are some:
1) Reference layer issues
2) Address Issues that can lead to inaccurate or failed geocoding?

A

Reference Layer
- A lack of standardization in sddress formats example, 54 W. 4th Ave. vs 54 West 4th Avenue etc.
- The currency of street network dataset
- Completeness of street network dataset (ie. missing ranges)

Address Issues
- Unusual Addresses ex. malls, P.O. boxes
- Misspelling
- Duplicate names and Aliases

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11
Q

What are the 5 characteristics of a network?

A
  • A set of linear features
  • Interconnected
  • With attributes
  • With constraints
  • There is flow or movement through the network
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11
Q

What are some examples of networks?

A
  • Roads
  • Sewer systems
  • Pipleines
  • streams
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12
Q

What are three GIS network applications?

A

Tracing, Routing, and Location-Allocation

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13
Q

Least-cost path vs traveling salesman problem

A

Least-cost path is routed through a series of stops in a user-defined order

Traveling salesman finds the most efficient sequence in which to visit all the stops

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14
Q

What is Location-Allocation?

A

Assigning portions of a network to facilities based on the ability of the facilities to meet the demand on their supply of resources. Example, schools, health clinics, distribution centers

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15
Q

Provide some examples of link, node, stop, and centre impedances

A

Link-> one-way traffic, speed limit, times of day
node-> traffic lights, stop signs, LHT vs RHT vs U-turn
stop -> service time, time windows (ex paring restrictions)
Centers -> max number of items at a location

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16
Q

What is linear referencing?

A

The method of storing geographic locations by using relative positions along a measured linear feature.

Distance measures are used to locate events along the line.

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17
Q

What are the 5 components of Linear Referencing?

A
  • The reference system - an objects relative location
  • Linear feature or route
  • distance along aka ‘measure’ aka ‘M value’
  • Point Events - stored in a event table as single M-values
  • Line Events - stored in event table as ‘From M’ and ‘To M’ values
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18
Q

Describe dynamic segmentation

A

DynSeg is the process of computing the map location (shape) of events stored in an event table

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19
Q

Advantages of linear referencing?

A
  • Avoids the physical segmentation of linear features
  • Updates to linear features are reflected in point and
    line event ‘M-Values’ => easier to update small
    sections of long segments without having to update
    entire segment
  • Events can be displayed and analyzed at run-time
    using Dynamic Segmentation
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20
Q

What are some uses for linear referencing?

A
  • Pavement type, speed limit, and # of lanes along highway using km from boundary
  • Pipeline material type recorded along a line in meters
  • Sediment type within a river reach recorded using river km.
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21
Q

What is a surface in relation to GIS?

A
  • Surfaces are continuous phenomena rather than discrete objects.
    -2.5D -> 2D + Z
    Z value is usually stored as an attribute and could be elevation, rainfall measures, soil samples etc.
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22
Q

Which would give the most accurate geocoding results-
Townships, ranges, postal codes, or census blocks?

A

Postal codes

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23
Q

Applications of elevation based surface analysis

A

-Terrain modeling / visualization
- Drainage networks
- Land development
- Slope stability

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24
Q

Describe Hillshade, viewshed, and Aspect

A

Hilshade is the visualization of a DTM showing shadows from sun’s position

Aspect is the compass direction of downhill slope

Viewshed is the visible areas from one or several points

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25
Q

What’s the difference between DSM, DTM, and DEM?

A

DSM = earth surface + built objects
DTM = just bare ground surface (no trees, buildings etc.)
DEM = generic term for both

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26
Q

What are the Primary and Secondary DTM data acquisition methods?

A

Primary
- Photogrammetry
- LiDAR
- Ground Survey
- Interferometry (electromagnetic waves)

Secondary
- Scanning or digitizing paper maps
- Converting existing digital data (ex griding contour data)

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27
Q

Describe point-based surface representation(s)

A
  • DEM/grid/lattice/point mesh- points can be either irregular distribution of x,y,z from field survey or regularily distributed
  • Irregularly spaced points must be interpreted into a grid(IDW, NN, Kriging, or Spline)
28
Q

What is interpolation?

A

converts know sample locations into a regularily spaced grid (DEM) or contours

29
Q

List and describe the 4 main interpolation techniques

A

1) Inverse Distance Weighting (IDW)
IDW assumes that each measured point has a local influence that diminishes with distance. It gives greater weights to points closest to the prediction location, and the weights diminish as a function of distance.

2) Nearest Neighbour
- Honours raw values- value of unknown point is
assigned the value of its closest known point

3) Spline
- Minimizes curvature
The spline interpolation method forces a smoothed curve through the set of known input points to estimate the unknown, intervening values.

4) Kriging
- Local interpolation method
- employs semivariograms of distance vs difference to interpolate the values of an input point layer and is more akin to a regression analysis
-Based on the concept that there is a trend or bias in the data, which can lead to erroneous (incorrect) interpolation

30
Q

True or False: A surface can be a raster or a vector dataset

A

True

31
Q

What are some line-based representations of surfaces?

A
  • Contours
  • TINs (can also be viewed as a surface)
  • Profiles
  • Breaklines (ridges, stream course, shorelines)
32
Q

What is a TIN?

A

Triangulated Irregular Network- consists of a series of non-overlapping, contiguous triangles generated from points (reg. or irreg. spaced) and can also incorporate breaklines

33
Q

What are thiessen / Voronoi polygons?

A

Define areas of influence around a sample point- all points within the area are closer to that sample point than to any other sample point

34
Q

What are the two steps to creating a TIN

A

1) Build Voronoi polygons
2) Create Delauny Triangles
- connect points between adjacent polygon faces
- maximize angles of triangles
- Nodes of triangles as close together as possible

35
Q

What is the Delaunay Criterion?

A

A circle drawn through three nodes of a triangle will contain no other nodes

36
Q

Compare and contrast TIN vs GRID for surface representation

A

TINs are more useful for;
- highly variable surfaces with irregularly distributed sample data
- representing the influence of streams, roads, and lakes (breaklines)
- examining localized areas (large-scale maps)

TIN drawbacks:
- They take longer to build and may require more disk space

Grids are more useful for;
- evenly distributed sample data
- examining large study areas (small-scale maps)
- load fairly quickly, simpler data structure -> less and easier storage and transfer

Grid drawbacks:
- bad at all the things TIN is good at

37
Q

Global polynomial vs local polynomial interpolation

A

Global
- Form of Trend Surface Analysis
- Uses all or most of the elevation data to characterize surface
at a point through a set of polynomial equations
- Best fit by minimizing the sum of the distances between the
know points and the surface
- first-order polynomial = flat plane / slope
- second-order polynomial = one bend = fitted to valley
- *Preserves terrain continuity and smoothness

Local
- Form of Curve or Surface Fitting
- Applies algorithm repeatedly to small portions of surface for
a good fit
- Interpolated elevation value of the point depends only on
neighboring data within each defined neighborhood
- Can capture short-range variations

38
Q

What are some uses of DEMs / DTMS

A
  • Sources of elevation data for digital topographic maps in national database
  • Cut and fill problems in road design and other civil engineering projects
  • Viewshed assessments for forestry- cutblock locations
  • A bunch more….
39
Q

What are the four scales of raster analysis?

A

Local
Neighbourhood / Focal
Zonal
Global

40
Q

What are the key characteristics of local raster analysis operations?

A
  • They are cell-based- operations are performed on every cell in the matrix/grid/surface independent of one another.
  • Can be performed on single or between multiple rasters
  • operations can be mathematical, relational (multi only) or logical (multi only)
41
Q

What is an example of a single grid local operation?

A

Converting slope values of a single raster from percent slope to degree slope

42
Q

Describe the outputs of local boolean operations on rasters- AND & OR

A

look at diagrams in slide -> hard to describe in words

43
Q

What are the key characteristics of Focal / neighbourhood raster analysis operations?

A

-Value of an output pixel is a function of the values of the neighbouring pixels defined by a moving window.

-Neighborhood functions examine the relationship of
an object with similar surrounding objects. They can be performed on point, line, or polygon vector
datasets as well.

-employ moving windows, also called filters or kernels, to calculate new cell values for every location
throughout the raster layer’s extent.

  • Overlapping neighbourhoods
44
Q

What are the key characteristics of Zonal / regional raster analysis operations?

A
  • employed on groups of cells of similar value or like features (zones)
    -Value of an output pixel is a function of the values of the zone pixels
  • May be applied to a single raster or two overlaying rasters.
  • single input raster -> zonal operations measure
    the geometry of each zone in the raster, such as area, perimeter, thickness, and mean.
  • two rasters -> one input raster and one zonal raster, a zonal operation produces an output raster, which summarizes the cell values in the input raster for each zone in the zonal raster

-non-overlapping neighbourhoods

45
Q

What are the key characteristics of Global raster analysis functions?

A
  • Value of the output raster is potentially based on the values of all the [pixels in the input raster.

Typical global operations include determining basic statistical values, such as mean, for the raster as a whole and assigning that value to all cells of the raster.

46
Q

What is enterprise GIS?

A

-GIS infrastructure shared by an entire organization or a group of affiliated organizations
- Used by multiple agencies / departments
- Public or private sector

47
Q

What is the essential goal of enterprise GIS?

A

To meet both the unique and common needs of a wide variety of stakeholders

48
Q

What are the six components of a GIS?

A

-hardware
-software
-data
-people
-process/methods
-network

49
Q

What are some challenges of implementing a GIS?

A
  • resistence to change
  • cost
  • doubt of the benefits
  • lack of understanding
  • organizational and personnel changes
  • data migration
50
Q

What are the 5 major stages of the Antenucci model for GIS? give a brief summary of the central goal of each stage

A
  1. Concept
    - defining user needs and requirements
  2. Design
    - developing a workable solution and implementation plan
  3. Development
    - acquiring GIS components and developing user applications
  4. Operation
    - Phasing from manual to automated activities
  5. Audit
    - evaluating operations and planning for the future

These 5 stages incorporate 17 steps

51
Q

List some possible reasons that a GIS Fails

A
  • Lack of flexibility in accommodating changing user needs
  • Difficulty in adapting software to other hardware/operating environments
  • Difficulty in modifying and maintaining software
  • Not focusing on key (critical) access factors
  • Lack of technical support
  • No defined goals and timelines
52
Q

Briefly describe the three methods for evaluating a GIS Implementation

A
  • Ad-hoc method:
    If time is limited, evaluate project based on your insight and previous interaction with clients
  • Cost-benifit alaysis
    Compare benefits to cost to determine weather the project is financially justifiable to move forward
  • Usability testing
    Test whether clients’ needs have been met; questionnaire, interview, observation
53
Q

True or false; inaccuracies, errors, and uncertainty can be introduced at all stages of GIS processing.

A

True

54
Q

Provide examples of possible sources of error / uncertainties for each of the four main stages of GIS processing

A

Data collection
- Sampling error

Data input
- scanning; resolution,
- data conversions
- editing - edge matching, cluster tolerance

Manipulation
- interpolation

Output
- Scaling and generalization

55
Q

Define Precision, Accuracy, Error, and Uncertainty

A

Precision: Variance of a value when repeated measurements are taken (reproducibility of the value)

Accuracy: how close a value is to the true value

Error encompasses both the imprecision of data and its inaccuracies.

Uncertainty is a catchall term to describe general geographic data representation.

56
Q

Describe and provide examples of Inherent Error

A
  • Inherent Errors occur as a result of being geospatial data
  • Generalization, selection, and symbolization all produce inherent error
  • Errors in map projections
  • Limitations in the accuracy to which data can be collected
  • The aging of data
56
Q

Describe operational error in general and provide examples of the three main types of operational error

A

occur during the process of collecting managing and using geospatial data

1) Gross- Imprecise mosaicking of adjacent aerial photos
2) Systematic: Operator bias towards recognizing a particular class, recording with too little precision, consistent error of an instrument.
3) Random: spike in data caused by a malfunction in the sensor

57
Q

Name and describe the three types of data standards.

A
  • De facto standard: Accepted by an industry doing something the same way. eg SHP files are a defacto standard for sharing spatial data
  • De Jure standard: developed by an organization empowered to create standards
  • Regulatory Standard: Usually De Jure standards that have been established by gov legislation and have legal enforcement
58
Q

What are the seven components of data quality?

A
  1. Lineage
  2. Positional Accuracy
  3. Attribute Accuracy
  4. Logical Consistency
  5. Completeness
  6. Temporal Accuracy
  7. Semantic Accuracy
59
Q

Which component of data quality answers questions such as Who collected the data? When was it collected, and why?

A

Lineage

60
Q

Describe the positional accuracy of data, and it’s two classes

A

A measure of the variance of the position of a mapped feature from the entity’s true position.

-is well-defined for standard mapping products from gov. agencies

1) Relative- a measure of the accuracy of individual features on a map compared to other features on the same map

2) Absolute- a measure of the location of features on a map compared to their true position on earths surface

61
Q

How is attribute accuracy evaluated?

A

May be done for primary data collection, but rarely done for secondary data
Field checks
Comparison with independent samples of higher order

62
Q

Describe logical consistency as it pertains to data quality

A

focused on attribute data and database integrity
3 main components
1) Correct domain values
2) Normalization
3) Completeness (no null data)

63
Q

Describe completeness as it pertains to data quality

A

Does all necessary graphic and non-graphic data exist within the database?
Evaluation of:
- Extent of datasets
- All necessary tables
- All layers present
- testing for entries in all necessary data fields
- checking level of detail in attribute classification

64
Q

Describe temporal accuracy as it pertains to data quality

A

the currency of features and their respective attributes

65
Q

Describe Semantic accuracy as it pertains to data quality

A

Defines the meaning of concepts within a data model by their relationships to other concepts. e.g transformers have to be connected to a power pole

66
Q

What form of documentation helps to resolve data quality problems?

A

Metadata

67
Q

What is a geocoding service?

A

A product/software that contains all the data, settings, and algorithms necessary to transform addresses and other text strings into map locations (geographic coordinates).

GIST 7100 - Fundamentals of GIS (1 decks)

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