Questions Flashcards
Who created or established the GISCI?
URISA
What kind of organization is GISCI?
Third-party non-profit
What makes GIS different from other professions/skills?
Among other things, GIS uses analysis to make determinations
What are the OGC File standards?
KML/KMZ, GML, OGC and ISO Simple Features, Geopackage, GeoTIFF, LAS
What are the OGC web-based standards?
WFS, WMS, WCS, WMPS, WPS
What geometry types are OGC standard?
Point, Curve, Surface. Point and curves include Line types, and surface includes polygons.
What standards does the FGDC publish?
Addressing, metadata, data quality, soil code, classification of wetlands, GPS accuracy, remote sensed data
What would be the NMAS horizontal value of a 1:150 scale map?
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.
What would be the NMAS horizontal value of a 1:625,500 scale map?
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.
What is the RMSE of a feature that is 5x and 7y away from its ground control?
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.
Is GIS Data Accurate?
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.
Is GIS Data Precise?
Location is ALWAYS precise, lengths and areas, if calculated by the software, are also precise. Attributes are always precise.
Can data be both accurate and precise, but incorrect?
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.
What is the digitizer precision constant for fuzzy tolerance?
0.002”
How to determine fuzzy tolerance value?
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
Which field is used for storing latitude and longitude values, and why?
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.)
What are the standards for raster accuracy according to the SDTS?
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.
What would you use to determine the accuracy and precision of a classified raster/land cover dataset?
Confusion matrix or Kappa coefficient, which utilize ground-truthing
What values do pixels hold?
Pixels typically store reflectance values of land cover until they are reclassified into “discrete” data
What metadata standards has the FGDC endorsed?
FGDC CSGDM, ISO 19115, ISO 19139
What is the most accurate representation of earth’s shape to the least accurate?
Geoid, spheroid ellipsoid, sphere
When is it okay to model the earth as a sphere?
Simplifies the math of creating less distortion; can be used on small scale maps smaller than 1:5,000,000
What is the shape of the earth?
An oblate ellipsoid (rotated around the minor axis, which means it bulges around the equator)
What is the difference in distance around the semi-major axis between the Clarke 1866 and GRS_1980 spheroids?
GRS_1980 is smaller by 69.4m than the Clark 1866
What is the preferred spheroid globally?
WGS84; the preferred spheroid in the US is GRS_1980, which NAD83 is based upon
What spheroid do GPS units use?
WGS84
NAD27’s point of origin
Meades Ranch, KS
NAD83’s point of origin
The approximation of the center of the earth
What are vertical datums? What are two examples of vertical datums?
A “zero surface” from which elevations are measured. NAVD88 and NGVD29
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.
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
What projected coordinate systems are used the most in the United States?
UTM and state plane, both in either NAD27 or 83
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
SRID/EPSG Code for NAD83?
4269
SRID/EPSG Code for NAD27?
4267
SRID/EPSG Code for WGS84?
4326
SRID/EPSG Code for WGS84 Web Mercator?
3857
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
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)
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.
When would you use geodesic measurements?
Distances on small-scale maps
When would you use planar measurements?
Distances on large-scale maps
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.
What map layout elements are absolutely required on any good map?
Title, Legend, scale, north arrow
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
In an RGB color map, what color would 255, 255, 255 be?
White
In an RGB color map, what color mapping would pure black be?
0, 0, 0
In an RGB color map, what color would 150, 0, 150 be?
Purple
Which 3 color maps are used to control color on a computer?
HSV, CMYK, and RGB
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.
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.
What is a choropleth map?
Polygons or other vector data are symbolized with colors