Midterm 1, Deck pt 1 Flashcards
Basics - Projections on Review Sheet
Which type of data is discrete
Vector or Raster
Vector
points/lines/polygons
T/F: A vector layer can include points, lines, AND polygons
False
one vector layer can include only one of the three
Vector data exists only when…
there is data there
It is only there if something exists there
Vector data consists of…
3 options
Points, lines, and polygons
What is a point
zero-dimensional, [x,y] location
What is a line
one dimensional, two points connected
1D, just distance, no area
What is a polygon
2 dimensional, lines connected to lines
2D, have an area
which is the most accurate? Points, lines or polygons?
points
because they have no dimension, they are just a place, infinitely accurate
What is remote sensing
gathering of data from a distance, typically from satellites
measure amount of EMR from a distance and then analyze and interpret it
Pros of remote sensing
unobtrusive, removes sampling bias through systematically collected data, helps to explain natural processes
cons of remote sensing
expensive, need expertise, can become uncalibrated, only collects superficial info (skin of the Earth)
What is Resolution
The detail we can get from remote sensing data
What are the four types of resolution
spatial, spectral, temporal, radiometric
what is spatial resolution
the physical size each pixel represents
also scale/grain
What is pixel heterogeneity
Different components represented within a pixel
The pixel is the average reflectance of all the components in the given area, the more components you have the harder it is to identify
what is spectral resolution
the number of spectral bands, measured in widths of the EMR
wavelengths and their spectral characteristics
the more spectral bands, the more complex the data
What is temporal resolution
how often a satellite captures the same area
with high being often, low being not often
what type of resolution do we lose at the expense of high temporal resolution
Spatial
Greyscale
what is radiometric resolution
the level of precision in your data
the digital number of possible brightness values, variability of brightness
what is raster data
A pixel grid of things that exist everywhere
every pixel (cell) contains a value to typically form an image and is given a scale to decide the resolution
Can we decide when/what a pixel represents in raster data
NO
There is always a value for everything, we do not decide what is and isn’t represented, something real is always there
What is scale
representative fraction, map distance : actual distance
coarse vs fine scale
coarse: larger area, more generalized
fine: smaller area, less generalized
large scale vs small scale
large: large representative fraction, more detail
small: larger area with reduced detail
large - lots of detail
small - very little detail
how is scale affected in GIS
it allows for limitless zooming in, because of the layers we can keep detail
what are the two types of maps
reference and thematic
general and special purpose (respectively)
what do reference maps include
geographical features, roads, boundaries, etc.
locations of physical features, and their boundaries/borders
what is the purpose of a thematic map
show the spatial distribution of data themes
types of thematic maps
choropleth, isopleth, continuous scale, dot maps, graduated symbols
what is a choropleth map
gradation in tones/shades of an area to represent data variability
choropleth maps and spatially….
spatially extensive
data value is equally true for whole area
data extends equally across whole space
(no matter where you are in alberta, the population of alberta remains the same)
choropleth maps and spatially…
spatially intensive
data is variable within the boundaries of a given area
population density of alberta is different throughout alberta
What is an isopleth map
lines connect points of equal value
contour maps and similar
good for generalizing point data
What is a dot map
each dot (symbol) represents a mapped feature
what is a continuous scale map
uses colour ramping of symbols to show both location and magnitude of a feature
intensity of colour or shade depicts magnitude
what is a graduated symbol map
(proportional symbol map)
uses sizes of a symbol to represent a range of values at various locations
we are more sensitive to colour changes than size changes
How do we decide how to classify data
you choose based on what you want your message to be from what you are representing, what you are trying to convince
common data classifications
equal interval, quantile, natural breaks, standard deviations
equal interval classification and pros/cons
split x-axis into equal percentile ranges
pros/cons: easy to understand but doesn’t always show variability or accuracy
Quantile classification
ranked list of data points where each category has same percentage of data
each class has same number of entries (25% of data, not 25% of x-axis)
Standard Deviations classification and pros/cons
take the mean and sd of data set, to measure the dispersion of the data
pros/cons: easy to defend based on statistical pattern, unbiased
natural breaks classification and pros/cons
Jenks breaks
look for obvious breaks between classes that represent meaningful differences
pros/cons: minimize variation w/in classes, maximize between, but not supportable with math or stats
Qualitative vs Quantitative
NOIR
No math can be done vs Math can be done (respectively)
NO/IR (respectively)
NOIR
feature grouping
Nominal, Ordinal, Interval, Ratio
Nominal Data
categories, unranked and unordered
apples, oranges, bananas
Ordinal Data
Ranked data but with no specific ranking interval, think order - they are in some arbitrarily decided order
doesn’t matter by how different the rankings are, just that they are
borderline qualitative/quantitative
Interval Data
known and consistent intervals, with no real zero
no real zero like 0 degrees Celsius
can add and subtract
Ratio Data
Known and consistent zeroes, with a real zero
0 Kelvin is a real zero
What does real zero mean (represent)
The absence of something, Nothing
How is nominal data represented
distinctive symbols for each category
how is ordinal data represented
categorized sizes
how is interval/ratio data represented
size and/or colour/tone
tone
shades of black
three dimensions of colour
hue, value, chroma
Hue
Actual shade
red vs blue vs green
qualitative, just meant to show difference
Value
Brightness (absence of black in a colour)
light vs dark
quantitative, lighter (brighter) = higher value
Chroma
Saturation/Intensity
pale green vs lime green
Qualitative
what is a developable surface
a shape that is flattenable, can be “unrolled” without distortion
cylindrical, conical, azimuthal (planar circle)
can be curved but in one direction only
what are the three developable surface aspects
orientation of surface to Earth’s axis
normal, transverse, and oblique
0 degrees, 90 degrees, anything else (respectively)
the two developable surfaces of secancy
tangent and secant
touches but doesn’t intersect, intersects the globe (respectively)
nature of the surfaces contact with the ellipsoid
3 main projections
conformal, equidistant, equal-area
conformal
preserves shape but distorts size
equal-area
preserves size (area), distorts shape
T/F: you can never have conformal and equal-area
True
equidistant
preserves distances between places
where is the least distortion
on the lines of secancy
what is georeferencing
the act of locating places
by coordinates, addresses, landmarks, etc.
three requirements for georeferencing
uniqueness, interoperability, persistence
one coordinate per location, has the same meaning across users, and coordinates do not change
2 coordinate systems
geographic and projected
lat/long locations on a sphere, reference to a plane then applied to a sphere
is UTM tangential or secant
Secant
It intersects the globe in two spots
how wide is a UTM zone and how many are there
6 degrees of longitude and 60 zones
what are the three things you need to locate something using UTM
Westing/Easting, zone number in N or S hemi., Northing/Southing
central meridian value of UTM
500000 m
Geoid
What gravity would to to Earth if it were fluid, bumpy and uneven but roughly mean sea level
Ellipsoid
smooth, mathematical, non-spherical model of the earth
what changes in an ellipsoid, latitude or longitude
latitude, it is no longer a measure of the angle to the center of the Earth, but to an equatorial plane
Datums
an area, point, or line used as reference for locating something
we can choose how we want them to fit the ellipsoid
What is the Alberta Township System
ATS
A map of land ownership, an Albertan version of the Dominion Land Survey
__ Meridians in Alta., traveling ___
3, West
“West of the 4/5/6 meridian”
Ranges run ___, for __ miles
East-West, 6
Roads run N-S
Townships run ___, for __ miles
South-North, 6
roads run E-W
Range roads and townships form squares of __ ________
(number and name of numbers)
36 sections
6x6 mile square, 1x1 mile section
1 section is split into ___ and each is called a _____ ______
16ths, legal subdivision
legal subdivion is a quarter mile by quarter mile
Order of ATS address
Legal Sbdv - Section - Twp - Rg - W of _ meridian
