GIS Exam 2

remote sensing

the acquisition of information about an object or phenomenon using

devices not in direct physical contact with what is being measured, ex: X-ray, MRI, aerial photograph

why remote sensing

allows a regional/national view (small scale), sees things invisible to the human eye, collects data on dangerous areas

passive sensor

only detect received light or light bounced off earth’s surface (space telescopes, drones with regular cameras)

active remote sensors

send out a signal and detects the bounce back (SONAR, RADAR)

remote data tends to be

continuous raster data (photography)

spatial resolution

the size of the smallest object that the remote sensor camera can detect, smaller=more detail

orthophoto

An image that’s been corrected for the perspective of the camera

electromagnetic radiation

Energy emitted and absorbed by charged particles that

exhibits wave-like behavior through space (radio waves, visible light)

black object

absorbs all wavelengths

white object

reflects wavelengths

blue, red, green objects

reflect the wavelength their color is (blue reflects blue)

spectral bands

narrow sections of the EMR (eyes have 3 cones, one cone per color band, green blue and red), light sensors work the same way

light used for remote sensing

visible, reflective, thermal, microwave

true color imagery

images how humans see them

infrared bands (imagery)

assign bands to colors you cannot see

photo interpretation

do you see what it is, or what you want to see

ground truthing

verifying measurements to ensure you interpret images correctly

direction

angle of difference between reference line (usually north) and a heading (straight line towards something)

azimuth

angle measured in degrees clockwise from north to a direction line out of 360, east is 90

back azimuth

opposite direction from a measured azimuth

true north (geographic north)

Earth’s axis of rotation

magnetic north

one end of the Earth’s magnetic field (125 miles away from true north)

grid north

North on a local grid coordinate system

declination

the angle of difference between True North and Magnetic North (hofstra 12 degrees W)

Correcting for Declination with Azimuths

When Mag N is west of True N, add the degrees (at hofstra add 12), When Mag N is east of True N, subtract the degrees

card

azimuths on it, numbers towards the edges

compass needle

magnetic part that points north

how to use rotating needle compass

align the needle with north, look across the center pivot, check degrees of object from north

orienteering compass

heading arrow, rotating card, point heading arrow at destination, rotate card so that it aligns with needle and heading arrow stays pointed at destination, record and direct for declination

great circle

circle that goes around the ENTIRE circumference of the Earth- all 24,000 miles, shortest distance between two points, azimuths constantly changing

Loxodrome / Rhumb line

a line with a constant compass heading (crosses each meridian at the same angle)

Loxodromes that are also great circle include

The equator, lines of longitude

bearings

heading angles given in degrees ranging only from 0° to 90°, (ex: N 45 degrees E or S 45 degrees W)

metes and bounds

A point-to-point outline of a parcel (unit of land) to define exactly where the parcel’s boundaries/edges are, expressed as distances and directions from succeeding reference, measured in bearings

metes and bounds information

deed (document who owns it) and property survey

elevation

the height of the land

mean sea level

average of all the low and high tides over a metonic cycle (19 years)

absolute relief symbols

Expressions of exact, numeric elevation, better for direct measurements, scientific work

relative relief mapping symbols

Qualitative impressions of elevation, quicker, at-a-glance impressions of relief, better for untrained map readers

absolute: spot elevations

a point with an elevation

benchmark (BM)

high accuracy spot elevation used by surveyors

absolute: hypsometric tinting

elevation by color

absolute: contour lines

lines of constant elevation

contour interval

vertical difference between contour lines

quantitative slope formula

rise (feet or meters)/run (miles of kilometers) (convert run to rise first)

relative: hachures

short lines that run directly downhill

relative: hillshading

light to peaks and shade depressions

digital elevation model (DEM)

raster data where each cell’s value is the elevation at that spot, valuable for what datasets we can calculate from them

Slope raster is where each box has a different elevation, where in aspect raster data each box has a different direction the slope is facing

slope raster v aspect raster

map projection

coordinate system that is flattened (stretched/shrunk/torn) for a flat medium such as paper

ways to categorize map projections

developable surface, what they distort

developable surfaces

planar, conic, cylindrical,

standard point/line

points or lines where theoretical the plane meets the sphere, making for no distortion

aspects maps can preserve

shape, area, distance, direction

preserving shape- conformal projections

tissot’s index dots same shape but different size

equal area (size preserving)

same size but weirdly shaped or other things

direction preserving

perspective sometimes at North Pole, much less common, can preserve this with one other aspect

distance preserving

preserves from a point, much less common than equal area or conformal

political aspects of maps

mercator projection is racist because it minimizes former colonies and maximizes small, rich, countries

gnomonic projection

any straight line follows great circle, planar, direction

mercator

cylindrical, preserves shape,

sinusoidal

equal area, good for thematic use

compromise projections

Preserve none of the four variables, good for world-scale reference or thematic use

classification

ordering or grouping attribute data into categories to be presented on a map

three decisions of classification

how many classes?, what method to use for placing?, what kind of graphic symbol

how many classes

qualitative map (classes differentiated by type, nominal and ordinal data), quantitative map (numerical data represented by amount, interval and ratio, choose the number [more than 2-3 but less than 8])

what method to use for placing the values into classes?

histogram: natural breaks, equal interval (equal attribute value range), quantile (equal number of states per class), manual

symbology

use of visual variables to communicate information

visual variable

property of a symbol/graphic mark that denotes a type of information (qualitative: hue/color, shape, text) (quantitative: size, line weight, color saturation, color value, pattern, orientation)

visual variables depend on

qualitative and quantitative maps

types of thematic maps

choropleth, dot density, graduated symbol

choropleth maps

different colors fill polygons by class (normalization to fix)

graduated symbol maps

data classed into symbol size classes,

dot density maps

dots represent a specific amount and use total data, placed randomly within each polygon

six core cartographic elements

title, credits, legend, scale, directional indicator, neatline/border

mercator projection, cylinder surface, preserves shape

gnomonic projection, planar/circular developable surface, preserves direction

azimuthal equidistant, planar/circular developable surface, preserves distance and direction

world plate carree aka equirectangular, cylindrical developable surface, preserves nothing

gall-peters, cylindrical developable surface, preserves area, anti mercator

Albers Equal Area, conic developable surface, preserves area

mollweide, pseudocylindrical developable surface, preserves nothing

winkel tripel, pseudocylindrical surface, preserves direction and distance