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ESPM 70 > ESPM 70 Midterm - Spring 13 > Flashcards

ESPM 70 Midterm - Spring 13 Flashcards

1
Q

What is GIS?

A

a system for manipulating spatial data in these ways:

  1. Entry and editing
  2. storage
  3. query and retrieval,
  4. transformation,
  5. analysis and display (soft copy) and
  6. printing (hard copy)
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2
Q

Is GIS only about maps or map making?

What is its difference from conventional maps?

A

GIS is about both maps and map making.

GIS hosts data that can be manipulated whereas conventional maps you cannot.

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3
Q

What are the FOUR - name three - driving forces (supporting disciplines) to GIS?

A
  1. Geography
  2. Statistics
  3. Computer Science
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4
Q

Give good examples where GIS is well suited

for use:

A

Local governance;

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5
Q

What are the popular coordinate systems

used in a GIS?

A
  1. Geographical Coordinate System
    - Longitude and Latitude
  2. Cartesian system - Universal Transverse Mercator (UTM system)
    - measured in Meters by Eastings (longitudinal distance) and Northings (latitudinal distance)
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6
Q

Can you tell the difference among “parallels”, “meridians”, “great circles”?

What is the shortest distance between two points on a spherical surface?

A

Great Circles: any circle whose center passes through the earth’s center.

  • any 2 points on a great circle has the SHORTEST SURFACE distance from each other.
  • Great circle therefore, has significance in navigation.
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7
Q

How are latitude and longitude defined?

A

Lines of latitude are drawn parallel to the equator as circles that span the Earth’s surface, they are measured in degrees
- there are 90 angular degrees of latitude from the equator to each of the poles.

Lines of longitude (or meridian) are circular arcs that meet at the poles. There are 180 degree of longitude either side of a starting meridian aka prime meridian

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8
Q

What is “datum”? What is “Geoid”?

A

“Datum” - a reference surface e.g. a site datum - a reference surface (there may be infinite reference surfaces) height against which elevations are measured

“Geoid” - is the surface perpendicular to a plumb line, and for which the pull of gravity is a given value. Its a MEASURED surface NOT mathematically defined.

  • Noted there are at least 3 definitions of “vertical”
    • a plumb direction
    • the center of the celestial disk
    • Perpendicular to the adopted ellipsoid
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9
Q

Name three major types of projections:

A
  1. Cylindrical Projection
  2. Conformal Projection
  3. Planar Projection
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10
Q

What type of map projection preserve direction?

What type preserves shape?

A

Cylindrical Projection preserves direction.

Conformal Projection preserves shape.

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11
Q

How do you find out which UTM zone a given latitude/longitude falls in?

A

In the UTM projection the transverse cylinder rotates by 6° increments, thus creating 60 (360° / 6°) strips or projection zones. In such a projection, instead of projecting the complete globe into a flat surface, each of the 60 strips or zones gets projected onto a plane separately, therefore minimizing scale distortion within each zone.

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12
Q

How are UTM coordinates defined?

A

By Easting and Northing :

The easting coordinate of a point is measured from the false origin 500000 meters to the west of the central meridian of the UTM zone. Within a zone, easting values increase towards east. A point lying 8 meters east of central meridian has an easting of 500000 + 8 = 500008mE. The easting of a point 350m west of central meridian would be 500000 – 350 = 499650mE.

A northing value in northern hemisphere specifies the number of meters a point is located north of the equator. The northing of a point south of the equator is equal to 10,000,000m minus its distance from the equator. In both northern and southern hemispheres, northing values increase from south to north.
– A point south of equator with a northing of 7587834mN is 10,000,000 – 7587834 = 2412166m south of the equator.

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13
Q

What can you tell about different state plane coordinate systems?

Do they have the same map projections?

A

Coordinates often in feet, sometimes in meters;
Arbitary origin;
Good for small area (little distortion), but you may need to cross zones.

They do not have the same projections.

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14
Q

Why do we need to do coordinate transformation?

How is coordinate transformation done?

A

We need to do coordinate transformation when digitizing from legacy maps or digitizing from suitable aerial photos.

Coordinate transformation is done through:

E = Te + a1(X) + a2(Y)

N = Tn + b1(X) + b2(Y)

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15
Q

How do you find out the UTM coordinate on a 7.5” quad sheet topographic map?

A

FInd out what the points are at and go from there with the Eastings and Northings

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16
Q

Why do we need ground control points?

What kinds of land marks make good GCPs?

How should GCPs be distributed in a map or image to be coordinate-transformed?

A

We need ground control points (GCP) for to calibrate model and also check the model.

Permanent landmarks make good GCPs

GCPs should be distributed into at least 3 in EACH quadrant with about 12-30 GCPs

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17
Q

Why high order polynomials are not necessarily good for transforming coordinates from one system to another?

A

They are not always good because surrounding areas may become distorted due to over-feeding. Therefore, error may be higher than lower order.
– BUT can be good with more GCPs!!

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18
Q

Is it always good to have smaller values in root mean squared errors (RMSE) in a coordinate transformation?

A

Yes, your goal is to fit transformation with a RMSE that is less than 5 meters.

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19
Q

How many types of GPS are out there in the world?

A

5 - 2 from U.S. and the others from different countries.

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20
Q

How much do you know about Navstar?

A

Early 1980’s

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21
Q

What is the minimum number of satellites required to unambiguously resolve a position in 3D on earth? Is the greater the number of satellites used in determining a position the better?

A

At least 21 satellites in 6 orbital planes with 12 hour return interval for each satellite. No, because the closer together they are the larger an area of uncertainty.

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22
Q

What is differential GPS?

How do you improve positioning accuracy if you do not have differential GPS positioning?

A

Differential GPS: Using two units to improve accuracy

  1. station set up over known position (“base”). Station set up at unknown point (“rover”)
  2. Collect data at both stations simultaneously.
  3. Calculate corrections from difference between base station known and measured position.

2 types:

  1. Post processed - highest accuracy
  2. Real time differential correctior - lower accu.
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23
Q

What is most popularly used database model in a GIS?

A

Vector Model

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24
Q

What makes geographic data different from ordinary data?

A

Ordinary data is discrete in space, where geographic data is a phenomena - continuous, not aerial base but viewed through triangulation.

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25
Q

Is a Topo map a thematic map?

A

No, Topo maps are general purpose maps. Thematic maps are organized around spatial distributions of specific information types. e.g. land use, census tracts and land power.

26
Q

What are the scales of measurement?

Can you explain them with examples?

A
  1. Nominal - by names e.g. the specific name of the type of soil
  2. Ordinal - descriptive e.g. med/high/low/or by percentage
  3. Interval - from one contour to another going up or down e.g. elevation: elevation with range between 0-5 ft or temperature
  4. Ratio - must have a real absolute value somewhere - an attribute regarding a FIXED location.
27
Q

What kind of models can one use to conceptualize space?

A
  1. Entities:
    - discrete objects, clear boundaries
    – Can make a grid network but measurements are taken at three points.
    Grid Cell Raster
    - empty space possible
  2. Fields:
    - continuously varying surface
    - space-filling
28
Q

What are the characteristics of a “vector-based” database VS a “raster-based” database?

A 
Vector based database vs. Raster:
1. Positional Precision
V -- Can be Precise 
R -- Defined by cell size
2. Attribute Precision
V -- Poor for continuous data
R -- Good for continuous data
3. Analytical capabilities 
V -- good for spatial query, adjacency, area, shape analyses. Poor for continuous data. Most analyses limited to intersections. Slower overlays. 
R -- Spatial query more difficult, good for local neighborhoods, continuous variable modeling. Rapid overlays. 
4. Data structures 
V - often complex
R - often quite simple
5. Storage requirements 
V - relatively small
R - often quite large
6. Coordinate conversion 
V - usually well-supported 
R - often difficult, getting easier
7. Network Analyses 
V - Easily handled 
R - often difficult
8. Output Quality 
V - very good, map like.
R - fine to poor - aliasing, can be good.
29
Q

What are the elements of Cartography?

A
  1. Projection - to minimize errors caused by flattening the earth’s surface
    - Map projection cause some distortion
  2. Scale: to present data in adequate level of details
    - Large scale maps need lots of paper
  3. Symbolization: to effectively communicate information from the map maker (cartographer) to the end user.
    - - allows you to effectively present the symbols on the map
30
Q

How many ways can you use in determining the scale of a map?

A

S = 1/Ground Distance/Map Distance

31
Q

How many types of scales can be used in a map layout?

When numerical scales fail to represent the scale of a map?

A

ANSWER

32
Q

Does scale change in one map?

Explain answer through a graphical sketch.

A

ANSWER

33
Q

What does minimum mapping unit mean?

A

MMU asks how small something is before eliminating it or margining it with other polygons.

34
Q

How is scale represented in raster data?

A

Cell size is the MMU - minimum mapping Unit
- spatial resoultion defines level of spatial detail in images - objects smaller than spatial resolution cannot be fully detectable – MIXED pixel problem

35
Q

What is a mixed pixel or a “Mixel”?

A

When objects cannot be detected in spatial resolution.

36
Q

What determines the amount of content represented in a map?

A

Depending on the purpose of your map and scale of map.

37
Q

What is map generalization?

Why should we care about map generalization in GIS?

A

Map generalization: Maps and geographic databases cannot contain all of the detail of real world:

  • depends on purpose of map
  • depends on scale of map

Map generalization is traditionally done from large scale map to compile smaller scale maps

38
Q

What is the primary factor determining the level of map generalization?

A

Scale of map

39
Q

Name at least FIVE types of map generalizations:

A
  1. Selection
  2. Simplification - weeding points to create simpler shape.
  3. Smoothing - replacing sharp/complex objects with smoother ones.
  4. Aggregation/merging - replacing many with fewer symbols.
  5. Collapsing - replacing area object with point or line.
  6. Displacement - moving to preserve visibility and distinctiveness.
  7. Merging - replacing several line objects
    with fewer
  8. Exaggeration - enlarging to preserve characteristics lost when shown at new scale.
40
Q

What is the difference between accuracy and precision?

Can you sketch out their differences?

A

Accuracy = Measurement - Truth
– or average of multiple measurement in reference to truth (target)

Precision - the closeness of measurements

    • it is determined by technology
    • it can be measured by standard deviation.
41
Q

What is a histogram?

What can you tell from a histogram?

Is a Histogram only limited to categorical data and nominal data?

A

SHows use the certain classes and the amount of frequency.

it’s a bar graph

yes.

42
Q

Can you explain the meaning of “mean” and “Variance”?

What is the relationship between variance and standard deviation?

How can one use such statistics in data classification?

A

“Mean” = the statistical average - sum of values for one attribute divided by the number of records.

“Std Dev” = average difference from the mean
- sum of mean substracted from the value for each record. squared, divided by number of records -1, square rooted.

Relationship between variance and std dev: without the square root in std dev = variance

You can use the statistics of std dev to show the disperision of data from the mean with low std dev = data disperse close to mean vice versa.

Variance shows the actually parameter of disperison of data.

43
Q

Why do we need classification?

A

By classifying we are assuming:

  1. discrete groups in distribution make sense/exist
  2. discrete units on landscape make sense/exist
    - - can apply to vector or raster data models.
    - - enforcing an “entity” view of space.
44
Q

Name a few strategies or types of data classification:

A

Wetlands; soil; forest fires

45
Q

Name a few geographic data sources:

A

USGS: digital raster graphics (DRG); digital line graphs (DLG); digital orthophoto quadrangles (DOQ)

46
Q

Where would you look for a land cover data?

A

NLCD

47
Q

Where you would you look for topographic, digital ortho quads or ortho images?

A

TIGER/Census data, USGS Digital Orthophoto Quadrangles (DOQ)

48
Q

Name a few applications of a digital ortho quad:

A

don’t know

49
Q

Where would you look for population data?

A

USDOC Census/TIGER Files

50
Q

Where would you look for wetland and soils data?

A

Wetland: USFWS National Wetlands Inventory (NWI
Soils: Digital Soil Data (National & State)

51
Q

How can you determine the elevation of a particular location in a topo map?

A

Elevation of a point between two contour lines: h = e1 + (e2 - e1) * AB/AC
- where “e” is elevation-

52
Q

What is a Voronoi Diagram?

A

Voronoi or Thiessen polygon: partition space into areas closest to each point is a Voronoi diagram.

  • one convenient way of converting point data to a real data
  • Approximate of continuous phenomena by points.
53
Q

What are the properties of Voronoi diagram?

A
  1. The dual graph for a Voronoi diagram corresponds to the Delaunay triangulation for the same set of points.
  2. The closest pair of points corresponds to two adjacent cells in the Voronoi diagram
  3. Two points are adjacent on the convex hull if and only if their Voronoi cells share an infinitely long side
54
Q

What is a Delauney triangle?

A

If you know Voronoi then you can get Delauney triangle // both vector data

55
Q

What is TIN?

A

Triangular Irregular Network (TIN) - Typically used to represent terrain or other spot-sampled continuous variables
- connect sample points in a network of triangles
Why? to preserve sample accuracy, save space.
**In TIN there are 3 parts:
1. Points - sample locations
2. Edges - connecting lines
3. Facets - triangles, “faces”
AND are 3 points on a circle AKA:
Convergent circles

56
Q

Name a few ways that we can use to represent elevation?

A

Contour lines;

57
Q

What kind of derivative parameters can we obtain from a DEM?

A

ANSWER

58
Q

Name a few ways that a DEM can be derived from:

A

Interpolated from digitized contours; interpolated from points (low relief); Gestalt photomapper, parallax on photopairs.

59
Q

Give an example of the fractal nature in geographic phenomena:

A

ANSWEr

60
Q

What can the fractal property of geographic objects be used for?

A

ANSWER

61
Q

In ArcMap, how to find the projection of the data frame (map) and the projection of individual data layers?

Is there any relationship between them?

A

ANSWER

62
Q

What are:

  1. clip
  2. intersect
  3. union
  4. selection by attribute and buffer operations

How can these operations be used in Suitability Analysis? (Lab 5)

A

These are common ways to apply: “Vector Overlays”.
1. Clip: cookie cutter approach, bounding polygon defines the clipped second layer. Neither the bounding polygon attributes nor geographic (spatial data) are included in the output layer.

  1. Intersection: COMBINES data from BOTH layers but only for the bounding area (bounding polygon ALSO defies the output layer data from both layers are combined Data outside the bounding layer (1st layer) is discarded)
    - Order of intersection is important!!
  2. Union: Includes all data from BOTH the bounding and data layers
    - New polygons are formed by the combinations of the coordinate data from each layer. (everything from both areas)

4.

ESPM 70 (1 decks)

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