Questions Flashcards
1
Q
Who created or established the GISCI?
A
URISA
2
Q
What kind of organization is GISCI?
A
Third-party non-profit
3
Q
What makes GIS different from other professions/skills?
A
Among other things, GIS uses analysis to make determinations
4
Q
What are the OGC File standards?
A
KML/KMZ, GML, OGC and ISO Simple Features, Geopackage, GeoTIFF, LAS
5
Q
What are the OGC web-based standards?
A
WFS, WMS, WCS, WMPS, WPS
6
Q
What geometry types are OGC standard?
A
Point, Curve, Surface. Point and curves include Line types, and surface includes polygons.
7
Q
What standards does the FGDC publish?
A
Addressing, metadata, data quality, soil code, classification of wetlands, GPS accuracy, remote sensed data
8
Q
What would be the NMAS horizontal value of a 1:150 scale map?
A
90% of at least 20 points need to be within this accuracy:
150” x 1/30”= X
150/30=5”
5”/12”=0.42’
So 90% of 20 points need to be within 5 inches or 0.42 feet of their actual place on the ground.
9
Q
What would be the NMAS horizontal value of a 1:625,500 scale map?
A
90” of at least 20 points need to be within this accuracy:
625,500” x 1/50” = X
625500/50=12,510”
12510/12 = 1,042’
So 90” of 20 points need to be within 12,510 inches or 1,042 feet of their actual place on the ground.
10
Q
What is the RMSE of a feature that is 5x and 7y away from its ground control?
A
RMSE=√(x1-x2)^2+(y1-y2)^2
RMSE=√5^2+7^2
RMSE=√25+49
RMSE=√84
Recall that PEMDAS is used when solving the equation.
11
Q
Is GIS Data Accurate?
A
Spatially, that will depend on the collection and entry methods. Measurements will be accurate if they’re collected by the software. Attribute accuracy also depends on the collection and data entry methods.
12
Q
Is GIS Data Precise?
A
Location is ALWAYS precise, lengths and areas, if calculated by the software, are also precise. Attributes are always precise.
13
Q
Can data be both accurate and precise, but incorrect?
A
Yes, where legalities are concerned. Perhaps legal measurements were taken with 3d or 2d surface in mind, or there is a slope involved. Always use legal values even over computational ones.
14
Q
What is the digitizer precision constant for fuzzy tolerance?
A
0.002”
15
Q
How to determine fuzzy tolerance value?
A
Determine:
1) the extent
2) resolution for data content (city, county, country etc)
3) the denominator that will give you the desired resolution: this will be the fuzzy tolerance value
16
Q
Which field is used for storing latitude and longitude values, and why?
A
Double; Single precision (Float) fields will only store up to 7 significant digits, while double can store 16. You need at least a scale of 6 (that is, 6 significant digits behind the period) to have an accurate lat and long coordinate, and up to 10 numbers in the precision field (9 if you include a - for W or S coordinates.)
17
Q
What are the standards for raster accuracy according to the SDTS?
A
Rasters should be reported at a 95% confidence level out of 20 check points distributed across the raster area. The distance between check point and corresponding raster point will depend on the scale of your display.
18
Q
What would you use to determine the accuracy and precision of a classified raster/land cover dataset?
A
Confusion matrix or Kappa coefficient, which utilize ground-truthing
19
Q
What values do pixels hold?
A
Pixels typically store reflectance values of land cover until they are reclassified into “discrete” data
20
Q
What metadata standards has the FGDC endorsed?
A
FGDC CSGDM, ISO 19115, ISO 19139
21
Q
What is the most accurate representation of earth’s shape to the least accurate?
A
Geoid, spheroid ellipsoid, sphere
22
Q
When is it okay to model the earth as a sphere?
A
Simplifies the math of creating less distortion; can be used on small scale maps smaller than 1:5,000,000
23
Q
What is the shape of the earth?
A
An oblate ellipsoid (rotated around the minor axis, which means it bulges around the equator)
24
Q
What is the difference in distance around the semi-major axis between the Clarke 1866 and GRS_1980 spheroids?
A
GRS_1980 is smaller by 69.4m than the Clark 1866
25
What is the preferred spheroid globally?
WGS84; the preferred spheroid in the US is GRS_1980, which NAD83 is based upon
26
What spheroid do GPS units use?
WGS84
27
NAD27's point of origin
Meades Ranch, KS
28
NAD83's point of origin
The approximation of the center of the earth
29
What are vertical datums? What are two examples of vertical datums?
A “zero surface” from which elevations are measured. NAVD88 and NGVD29
30
What is the principle difference between geographic coordinate systems and cartesian coordinate systems?
Geographic coordinate systems are based upon 3D measurements on the earth’s surface with units in decimal degrees; Cartesian or projected coordinate systems are 2D measurements that are in units of distance.
31
What are the 4 distortions introduced by projections, and what type of words are used to explain different PCS that minimize these distortions?
Shape: Conformal
Area: Equal area, equivalent
Distance: Equidistant
Direction: Transverse Mercator, Azimuthal
32
What projected coordinate systems are used the most in the United States?
UTM and state plane, both in either NAD27 or 83
33
What two projections are used in State Plane grids?
Transverse Mercator for tall states, Lambert Conformal Conic, used for broad states; SPC 83 is typically in meters not feet
34
SRID/EPSG Code for NAD83?
4269
35
SRID/EPSG Code for NAD27?
4267
36
SRID/EPSG Code for WGS84?
4326
37
SRID/EPSG Code for WGS84 Web Mercator?
3857
38
What is the difference between an international foot and the US foot?
US feet don't round off the fraction like an international foot does. This can cause a problem over a large area
39
What is the difference between map units and display units?
Map units are used for the page or a screen (inches, cm) whereas display units are on the ground (feet, meters)
40
How would you measure the distance that an airplane would have to fly around the earth?
You would take into account the geodesic distance, which takes into account the curvature of the earth. If earth is considered as a sphere instead of an ellipsoid, those distances are called great circles.
41
When would you use geodesic measurements?
Distances on small-scale maps
42
When would you use planar measurements?
Distances on large-scale maps
43
Can you calculate area in lat/long?
No, a degree is an invalid distance or area unit because it changes based on the projection and coordinates.
44
What map layout elements are absolutely required on any good map?
Title, Legend, scale, north arrow
45
What map layout elements are secondary to any decent map, as in just "nice to have"?
Coordinate system info, Author's name/org, logo, print date, Graticule and/or grid
46
In an RGB color map, what color would 255, 255, 255 be?
White
47
In an RGB color map, what color mapping would pure black be?
0, 0, 0
48
In an RGB color map, what color would 150, 0, 150 be?
Purple
49
Which 3 color maps are used to control color on a computer?
HSV, CMYK, and RGB
50
When designing a multivariate display, in what drawing order would you display vector data? What about a combination of both raster and vector data?
For just vector data, you would first put points, then lines, then polygon files. For a combo of raster and vector, you would always place the raster on the bottom.
51
What is the difference between graduated symbol vs. proportional symbol?
With graduated symbols, each symbol represents a range or class where each possible value is grouped into a class, but in proportional symbols, each dot represents an observation with the size of the dot relative to the size of the value compared against the dataset.
52
What is a choropleth map?
Polygons or other vector data are symbolized with colors
53
What is a heat map?
Heat map shows a concentration of values by adding more color to the area; is also a good way to generalize sensitive data
54
What are lines of indefinite measure, usually used in flatter terrain called?
Supplemental lines
55
What are lines of equal value that represent rainfall, air pollution, noise or other less tangible attributes called?
Isolines
56
What does it mean when contours are squished together?
Area of quick elevation change, whether it be a depression or a hill
57
What are some examples of non-continuous/discrete raster surfaces?
Scanned maps, or land use classification rasters
58
Does a centroid have to be inside of a polygon?
No, the centroid represents the center of the feature’s weight, so if a polygon has an irregular shape or is part of a multipart feature, then the centroid can fall outside of the shape boundary.
59
What is a vector relational database? An object-oriented relational database?
Shapefile; geodatabase
60
What are examples of raster file types?
tiff, jpg, bmp, Sid, img, bil, bip, ESRI GRID, gif, png, emf and pdf
61
What are some terms surrounding TINs that are helpful to know?
Triangulated Irregular Network, Wire frame model, Delaunay Triangulation, edges
62
What are some examples of 3D data types?
Vector data with z values; raster single band with z values; TINs; multipatch or multipoint; point clouds, LiDAR
63
What is the difference between QA and QC?
QA is proactive about putting standards in place to prevent quality deterioration, whereas QC is reactive and goes back to check the output or results after or during collection
64
What is an example of raster quality control to check to see if the raster matches its depicted area?
Ground truthing, which should be done on 20+ points at 95% accuracy
65
Can you represent accurate lat/long values with a float field?
No, latlongs require a double precision field with at least 9 precision
66
What are the three grades of GPS units?
Consumer/Recreational grade, mapping grade and survey/military grade
67
What is the discipline that measures away from known points called benchmarks or control stations, to gather new points?
Surveying
68
What are some examples of differential correction?
RTK, SBAS, VRS
69
What are some examples of geodatabase topology?
Make sure that valves and pipelines are connected; Check that political zones are covered by provinces; verify that property boundaries do not overlap; ensure there are no gaps between city council districts
70
What is uncertainty in regards to data?
How sure are we that our data is an accurate representation of real-world features? Also called "noise" in raster classification.
71
How do you know that data is georeferenced?
It will be in a geographic coordinate system or projected coordinate system (degrees, lat longs or distance units)
72
When would you use COGO over something like tracing?
You would use COGO if you wanted to draw something in based on its metes and bounds or legal description. For instance, if there's a parcel or property line defined.
73
Why should you not georeference to an unprojected basemap?
You will run into distortion because most images you georeference are projected to a 2d surface already
74
Suppose your basemap and your scanned map are in different coordinate systems. What should you do when georeferencing the scanned image to that basemap?
You should change your basemap to the image coordinate system, georeference the image in, then you can change the data frame back and the image will correct accordingly
75
What file types or extensions store georeferencing info?
Sometimes stored in the header of the image file; a separate ASCII world file such as tfw (often end in a w for world file)
76
What is the difference between a transformation and "rubber-sheeting"?
Translation allows for transformations of the image, such as rotate, scale, shear etc, while rubber-sheeting is used to sort of "drape" the image over a surface, but is not coordinate-bound, and is used for less geographic-specific uses like AutoCAD or hand-drawn images.
77
What is the order of priority for georeferencing files or information?
1) Header file (if supported), 2) the world file, and 3) the row/column info of the image
78
Who started the Global Positioning System?
United States DoD in 1973; it became public in the 80's
79
How often do the GPS satellites orbit and how far away from earth's surface are they?
Satellites orbit the globe twice a day, at about 12,000 miles above surface
80
How many satellites do you need to calculate an accurate horizontal location? Vertical location?
3 for horizontal (2D point), 4 for vertical (3D point), this is what "triangulation" refers to in context of locating your receiver
81
What are some common GPS errors to note?
Noise, Atmospheric Distortion, Distance from Base Unit, Selective Availability
82
What is Selective Availability in regards to GPS?
Selective Availability is the US military's ability to degrade signals for civilians; it's turned off right now.
83
What is the main difference between other "contain/within" queries and Clementi queries?
For Clementi queries, features sitting entirely on a boundary will be excluded from the selection.
84
What is the difference between Intersect and Clip?
Clip keeps only the target features attributes and common geometry, intersect combines attributes and geometry from overlapping input features.
85
What is the difference between Intersect and Union?
Intersect only gives you attributes from the overlapping areas of all features, whereas union will give all of every "united" feature, regardless of overlaps.
86
What kind of overlay analyses are there, and how should they be used?
There is the site suitability matrix, which you would use to determine based on multiple overlays (factors) which site is best suited for your purpose; Risk assessment would be for the same reasoning; Use weighted values for each layer, where 1 is completely suitable and 0 is completely unsuitable
87
How many layers and what kind should you use for an overlay analysis?
Two or more, and the more layers you use, the better and more specific your outcome will be; you can use polygon and/or raster layers.
88
Why would you want to generalize your map or data?
Generalization is useful when decluttering small scale maps, to make a dynamic map draw faster, or to protect privacy interests by reducing details of data.
89
What are some ways you can generalize data?
Hotspot mapping; scale-dependent display settings; Simplify lines or polygon boundaries; combining polygons or creating them to show clusters
90
What does the following equation evaluate to?:
| 3/4(8+4)(7-4)
```
PEMDAS:
3/4(8+4)(7-4)=x
3/4(12)(3)=x
3/4(36)=x
108/4=x
27=x
```
91
What does the following equation evaluate to?:
| 3(4+2)-(3-7)
```
PEMDAS:
3(4+2)-(3-7)=x
3(6)-(-4)=x
18+4=x
22=x
```
92
Calculate the percentage of houses burned:
| 80 houses in town were burned in recent fires. There were 240 left undamaged.
```
80=x/(240+80)
80=x(320)
80/320=x
0.25=x
25% of the houses were burned
```
93
Convert 35.72° to DMS
Leave 35 since it is whole
0.72x60(mins) = 43.2'
0.2x60(secs)=12"
So 35.72° = 35° 43' 12"
94
Convert 25° 15' 30" to DD
Leave 25 since it is whole
15/60 = 0.25°
30/3600= 0.0083333°
25+.25+0.0083333=25.2583333°
95
pi/4rad = x°
180°/4 = 45°
96
What is the MAUP?
Modifiable Aerial Unit Problem; in short, results can be different for the same dataset if you change the scale or shape of the zone that you're studying.
97
What are different examples of rasters?
Remotely-sensed imagery, surfaces, scanned maps, classified images (remember: just because something is a raster doesn't mean it's continuous, rasters can be discrete as well)
98
What is IR and what is its use case scenario?
IR is infrared wavelength imagery that senses heat signatures rather than color; you can use it to show forested areas, agriculture, flora health, flood assessment and military uses; they also can be displayed as false-color composites
99
Which kind of LiDAR quality value is the least expensive and probably the oldest data? Which is the highest quality stuff? Which is required by the 3DEP program?
The oldest and least-dense LiDAR info is Q3; Q0 is the highest quality, but 3DEP requires at least Q2 LiDAR info.
100
What values can raster grid cells contain?
Each cell contains one pixel value, can either represent a color or an elevation; may be positive or negative, integer or floating point, or single-band or multiband.
101
What is lossless compression of raster imagery?
LZ77 run-length encoding
102
What is lossy file types of raster imagery?
JPEG 2000; MrSID, ECW
103
What is a single-band raster called? Multiband?
DEM, elevation file; Aerial, imagery
104
What is the difference between an integer and floating point raster?
Integer rasters are discrete and have an attribute table; are typically used for classified data; floating point rasters are truly continuous and do not have attributes, are typically used for surfaces
105
What is a 1-bit raster?
These are binary rasters as each cell can hold a value of only 0 or 1
106
What is the bit depth potential for rasters?
Rasters can be between 1 - 64 bit
107
How to rasters store georeferencing information?
Some rasters store the georeference info directly in the header files, others can use world files, and a few types can do both.
108
What are raster "Pyramids"?
Pyramids generalize rasters for display purposes, so that they don't overload the graphics card or software you're displaying the raster on
109
What file extension/type would you store extra raster information, such as color map, statistics, histogram, tables, coordinate system, projection, or pyramid?
.aux or .aux.xml file
110
What is the resampling technique used for continuous rasters that will give you the smoothest appearance to your output?
Bilinear Interpolation
111
What resampling technique is default in ArcGIS, and is useful for discrete rasters?
Nearest Neighbor
112
What resampling technique is useful for continuous data, but will give you a sharper appearance than Bilinear Interpolation?
Cubic Convolution
113
What resampling technique is useful for discrete rasters, but will give you a smoother appearance than Nearest Neighbor?
Majority
114
What tool is used for raster Map Algebra in ArcGIS?
Raster Calculator
115
What is the field that relates two tables in a relational database called?
Key (Primary Key)
116
What is the field that is the unique identifier inside of a table called?
Foreign Key
117
What are considered "non-relational databases"?
NoSQL databases such as MongoDB; Microsoft Access (can be used as relational, but access itself is just the front-end)
118
What kind of cardinality is the following statement an example of? "One parcel has one owner." What function is appropriate here?
One to One; Join and Relate
119
What kind of cardinality is the following statement an example of? "One parcel has many owners." What function is appropriate here?
One to Many; Relate
120
What kind of cardinality is the following statement an example of? "Many parcels have the same owner." What function is appropriate here?
Many to One; Join and Relate
121
What kind of cardinality is the following statement an example of? "Many parcels have many owners." What function is appropriate here?
Many to Many; Relate
122
When speaking of cardinality, what term explains the Key from the parent table? Key from the child table?
Origin and Destination
123
Is historical data static or dynamic?
Static
124
What is the difference between an archive and a backup?
Backups are used as short-term safety nets to protect active data, whereas archives take copies of data and place them off of the main disc, often used for inactive data.
125
What are a few ways you can optimize your database?
Database compression, indexing, GIS Database Optimization
126
Why should you use UNC naming over sourcing from the letter drive?
UNC naming works better as some users won't have their network locations mapped the same way you do (for instance, maybe they don't have P:\ drive mapped)
127
What are Agile vs. Waterfall development methods, and which are used most often these days?
Agile developing develops programs in sprints, coming out with updates or patches after the initial launch of the software, whereas waterfall approach develops the product all at once and typically does not release again. Agile is used most often these days (for instance, OS updates, patches, etc)
128
What does server-side mean? Client-side?
Server-side refers to the process or execution happening on the inside of a firewall, with the server machine; client-side refers to the process or execution happening on the requestor machine, in the browser.
129
What is the difference between a virtual machine and a virtual private network?
VMs are logged into remotely from any computer given you have proper authorization, and multiple users can be using their own instance on a single machine; VPNs are a tunnel from a remote computer into a private network. Generally, VMs are much more efficient than VPNs.
130
Out of the following list, which services are secured?: HTTP, HTTPS, LDAP, SFTP
Https and SFTP are secured services
