GIS Quiz One

Geospatial Technology

The use of systems and tools that acquire, manage, store, or visualize location based data

Geographic Information Systems (GIS)

Software to store, analyze, and map spatial data.

Remote Sensing

Gathering Data from a distance - satellite imagery and aerial photography

Global Positioning System (GPS)

A satellite network that pinpoints location on earth

Spatial Data

• Describes WHERE something is on Earth

• Tied to coordinates, boundaries, or a place

Non-Spatial Data

• Describes WHAT something is

• The characteristics attached to a location

• Can be linked to a location

The National Map

Provides a “one-stop-shop” for free geospatial data

Geography

It deals with both the spatial characteristics of the planet and also the spatial relationships and interacts with the people and features that occupy it

Geographic Information Science

Study of concepts related to how spatial data is handled

Geotag

The ability to note your location within a piece of media, such as a photo or post.

Geodesy

The science of measuring the Earth’s shape, size, and gravitational field

Datum

A reference framework - a model of the earth’s shape - used as the basis for locating position

Ellipsoid

A smooth mathematical model of the Earth: a sphere slightly flattened at the poles

Geoid

A model based on mean sea level and gravity - The Earth’s true, slightly lumpy shape

North American Datum of 1927 (NAD27)

Datum built on the Clarke 1866 ellipsoid and anchored at Meades Ranch, Kansas. The older standard for U.S. maps.

North American Datum of 1983 (NAD83)

An earth centered datum designed for the satellite era - the current standard for North America

World Geodetic System of 1984 (WGS84)

A global, earth centered datum. This is the datum GPS uses worldwide

Latitude

• Runs east to west

• 0° at the equator to 90° at the poles

Longitude

• Runs north to south

• 0° at the Prime Meridian to 180°

• The 180° line is the International Date Line

Decimal Degrees = Degrees + (minutes/60) + (seconds/3600)

What is the formula to convert Degrees, Minutes, Seconds to Decimal Degrees

15

_____ degrees of longitude starts a new time zone

1.15

There are ______ miles per one minute of latitude

1.15 miles

How many miles is one nautical mile

Cylindrical

What type of projection is this?

Conical

What type of projection is this?

Azimuthal

What type of projection is this?

Mercator Projection

Conformal - Keeps shape and angle; area grows toward the poles

Sinusoidal Projection

Equal-Area - sizes are true, but shapes shear away from the center

Equal-Area Cylindrical Projection

Equal-area - Sizes are true, shapes are squashed at high latitudes

Robinson Projection

Compromise - Neither exact, but both look near-right in the mid-latitudes

Datum

• A foundation and reference frame for measurements

• Fixes where position sit in 3-D relative to a model of the Earth

• Answers: “measure relative to what”

Projection

• A two-dimensional representation of a 3D

• Draws those 3D positions onto a flat map - and always adds some distortion

• Answers: “how do we show it flat?”

60 zones

The world is divided into ___ ______, each of them being 6° of longitude wide.

cylindrical projection

Each zone gets its own ______ ________ to keep distortion low

False Easting

Each zone’s central meridian is set to an easting of 500,000 meters. Locations east of it add meters; west of it subtract - so values never go negative

False Northing

In the southern hemisphere, the equator is set to 10,000,000 meters and values count down going south - again avoiding any negative coordinates

Universal Transverse Mercator (UTM)

60 metric zones, each 6° wide, worldwide

Universal Transverse Mercator (UTM)

A worldwide metric grid

State Plane Coordinate System (SPCS)

State-by-state high accuracy zones

Reproject

Change data from one projection/system to another

Spatial reference

A real-world coordinate system used to identify locations. It ties data to an actual place on Earth

Georeferencing

Aligning an unreferenced dataset with one that has spatial reference information

Reproject

• The data ALREADY has a spatial reference

• You’re converting it from one system to another

• Math is known - The software just transforms coordinates

Georeference

• The data has NO spatial reference

• You’re assigning it real-world coordinates for the first time

• You pick control points and then the software solves the fit

Ground Control Points (GCPs)

The tie spots where coordinates are known. They connect the unreferenced data to the source and anchor the whole alignment

Rotation

Skewing

Translation

Scaling

Root Mean Square Error (RMSE)

Measures how well your data lined up - The lower the better

X=Ax+By+C; Y=Dx+Ey+F

What are the equations for the Affline Transformation

Resampling

Recomputing pixel locations/values after warping

Road intersections, Building Corners, Well-defined and findable in both datasets, doesn’t change over time

What would make a good control point?

The U.S. Department of Defense

Who made GPS?

U.S. Navy Transit & NRL Timation

The “GPS” in the 1960’s

The 2nd Space Operations Squadron

Who runs the NAVSTAR GPS today?

GPS

• The U.S. NAVSTAR system specifically

• Free and available worldwide

• Just one of Several such systems

Global Navigation Satellite System (GNSS)

• The umbrella term for all systems

• Includes GPS, GLONASS, Galileo, BeiDou, & and more

Space segment, Control Segment, and User segment

What are the 3 segments of GPS

Space Segment

The satellites in orbit broadcasting signals

24

How many satellites make up a full constellation

Control Segment

The ground crew that helps keep the satellites readings stay true

User segment

Involves any receiver - a one-way listener

Almanac

The general status and orbit data for the satellites, included in the broadcast

Ephemeris

More precise data on a satellite’s exact position in its orbit

C/A Code

Coarse acquisition - on L1; the code that civilian receivers use

P Code

Precise - on L1 and L2; more accurate, requires a military receiver

Y Code

An encrypted version of the P code (anti-spoofing)

M Code

A newer military code, more resistant to jamming

Distance = time x speed of light

What is the formula to find distance

Trilateration

3 distances are used to pin down one location

Differential GPS (DGPS)

A base station at a precisely known location measures the GPS error and broadcasts a correction to nearby receivers

Continuously Operating Reference Stations (CORS)

What provides differential corrections across the U.S.

Satellite Based Augmentation System (SBAS)

Sends the correction from an additional satellite instead of a ground station

WAAS

The FAA’s SBAS for North America - Ground stations feed geostationary satellites that broadcast a correct. Cuts error to 3 m or less

Europe

What region uses EGNOS and Galileo

India

What region uses GAGAN and NavIC/IRNSS

Japan

What region uses MSAS and QZSS

Russia

What region uses GLONASS

China

What region uses BeiDou

Geocaching

Small objects are hidden and their coordinates are posted online. You then use a GPS receiver to track them down

Multipath

Errors from signals bouncing off surfaces

Position Dilution of Precision (PDOP)

Error from poor satellite geometry - lower is better

Selective Availabilty

Intentional degradation of GPS accuracy - it was turned off in 2000

Sinusoidal

What projection is this?

Mercator

What projection is this?

Equal Area Cylindrical

Which projection is this?

Robinson

Which projection is this?

Universal Transverse Mercator (UTM)

What does this image represent?