GIS Quiz 1 - Coordinate systems, GPS, general overview

4 Aspects of Geographic Information

typological attribute, location attribute, spatial topology, time

typological attribute

the ‘what’ (lake, parking lot, income, population)

represented by number/label/symbol

every location has numerous such attributes

location attribute

the ‘where’

represented by address/coordinates, etc.

spatial topology (spatial dependence)

inside, adjacent to, north to, certain distance from

time

for dynamic spatial modeling, weather, climate, landuse change, real time transportation control, etc

coordinate system

a pair or triplet of numbers that specify location with reference to some origin

geographic coordinate system

based on spheroidal (either truly spherical or elliptical) surface that approximates the surface of the earth

datum

reference system or an approximation of the earth’s surface against which positional measurements are made for computing locations

coordinates (ex: latitude + longitude) in a geographic coordinate system are referred to as?

a datum

latitude

HORIZONTAL, parallels

equator = 0 deg lat

circumference of parallels varies

1 degree latitude = 111 km

longitude

VERTICAL, meridians

defined by planes that pass thru earth’s spin axis

prime meridian = 0 deg long

1 degree longitude = 111 km, 0 km at poles

horizontal datums

used for describing a point on the earth’s surface, in latitude and longitude or another coordinate system

vertical datums

are used to measure elevations or underwater depths

ellipsoid

used as an approximation of the earth’s shape

oblate ellipsoid

a sphere that has been flattened slightly at the poles

earth’s geoid

the shape that the surface of the oceans would take under the influence of earth’s gravitation and rotation alone (no wind and tides)

model of global mean sea level (0 elevation)

used to measure precise surface elevations

latitude and longitude are defined using an ____?

ellipsoid

elevation is defined using the ____?

geoid

earth datums define standard values of the ___- and ____

ellipsoid and geoid

coordinate overview

accurate depiction of location depends on the shape of the earth

elevations are relative to the earth’s shape

we model the shape of the earth as an oblate ellipsoid

projected coordinate system

method for representing a spherical or curved surface on a flat plane

series of mathematical transformations that convert location of points on a curved surface to locations on a flat plane (requires a datum because projected coordinate systems are based on geographic coordinates)

types of projections

cylindrical, azimuthal/planar, conical, etc

cylindrical projection

easy to use

latitude and longitude at right angles

shows true direction

distorts high latitudes

azimuthal/planar projections

useful for polar regions

distorts direction and distance

conical projections

useful for showing small areas accurately

universal transverse mercator

each zone has a central meridian located at exactly the middle of the zone

point of origin in each zone is the intersection of the zone’s central meridian and the equator

to avoid negative coordinates, the central meridian of each zone is set at 500,000 m East

UTM zones in the US

UTM is designed to cover whole earth (except for arctic + antarctic)

NJ —> UTM Zone 18 North (72 deg W - 78 deg W)

GPS

global positioning system

only system able to show you your exact position on the earth anytime, in any weather, anywhere

3 parts of GPS:

satellites, receivers, software

satellites usage

satellite TV, cellular phones, military purposes, etc

time difference

GPS receiver compares the time a signal was transmitted by a satellite with the time it was received.

time difference tells the GPS receiver how far away the satellite is

if it took 0.06 s to receive a signal transmitted by a satellite, find the distance from the satellite:

186,000 mps x 0.06 s = 11,160 miles

trilateration

1st satellite: locates you somewhere on a sphere

2nd satellite: narrows your location to a sphere created by the intersection of the two satellite spheres

3rd satellite: reduces the choice of 2 possible points

4th satellite: helps calculate a timing and location correction and selects one of the remaining two points as your position

how position is measured

atomic clocks

used by GPS satellites for accuracy, but not by most GPS receivers ($$$)

line of sight transmissions

ability to draw a straight line between 2 objects without any other objects getting in the way

GPS transmissions are line of sight transmissions

PDOP

positional dilution of precision

lower, the better the accuracy

what does GPS transmit

time and distance information 

what affects accuracy of GPS?

timing and PDOP

GIS

geographic Information systems

computerized systems designed for storage, retrieval, and analysis of geographically referenced data

uses advanced analytical tools to explore at a scientific level

John Snow

mapped cholera outbreak in London

what does GIS answer?

location - what and where

condition - status of features

trends - what has changed since…?

patterns - what spatial patterns exist?

modeling - what if…?

large scale map example

zoomed in

city maps, street maps

small scale map example

zoomed out

map of the earth

raster data

stored electronic image or picture taken as an aerial photo or satellite image

vector data

map features (points, lines, polygons)

feature attributes (every feature has attributes (name, area, population))

Roger Tomlinson

Father of GIS, created Canadian GIS

Canadian Geographic Information System

First computerized GIS

Assisted in regulatory procedures of land-use management and resource monitoring 

Made by Roger Tomlinson

Jack Dangermond

Founded Esri with his wife Laura

weather

short term state of the atmosphere in a specific place at a specific time

weather examples

temp, humidity, precipitation, wind speed, cloud cover, atmospheric pressure

how to predict weather

observations (weather stations, satellites, weather balloons)

patterns and historical data (meteorologists identify trends)

remote sensing (satellites)

high pressure (anti cyclone)

air sinks, creating high pressure at the surface

high pressure system characteristics

air sinks, warms, and dries; clear skies

sunny dry conditions

low pressure (cyclone)

air rises, creating low pressure at the surface

low pressure system characteristics

rising air cools and condenses, forming precipitation

brings clouds, rains, storms

fronts

boundary between 2 air masses of different temperature and density

cold front

cold air mass moves into a region of warmer air

cold front characteristics

cold air is dense, and wedges under warm air. this forces it up

rapid lifting = rain + thunderstorms

moves faster than warm fronts

warm front

a warm air mass moves into a region of cooler air

warm front characteristics

warm air slowly rises over cold air

clouds gradually form

creates overcast, steady rain, gradual warming

thunderstorm formations

warm moist air rises rapidly (convection)

air cools as it rises —> water condenses + storm develops

hurricane formation conditions

warm ocean (gives energy)

low pressure over ocean

high humidity in lower atmosphere

hurricane formation steps

1. tropical disturbance (cluster of thunderstorms over water)

2. tropical depression (organized system of clouds and thunderstorms)

3. tropical storm (high wind speeds; gets named)

4. hurricane (higher wind speeds, eye forms

low pressure + warm/moist air

storms, rain

cold front + rising warm air

thunderstorms

high pressure + sinking air

clear skies

warm ocean + low pressure disturbance

hurricane development