GIS Test 2
Interpreter Assisted Map
a map shown to the audience by an interpreter; they orally discuss the aspects of the map (ex: weather maps on TV)
Stand-Alone Map
a map that is easily interpreted by an audience
Control Points
one-to-one relation between points (points on the map projection may come from a map or survey in field)
North Arrow
provides orientation for the reader, important for maps of small areas and should be placed near the scale bar
relative height
Does GPS measure actual or relative height?
Trilateration
Does GPS use triangulation or trilateration to determine location?
Establishes: The Federal Geographic Data Committee (FGDC) National Geospatial Data Clearinghouse (download and submit data for others) Standardized documentation of data Public Access to geospatial data
Executive Order 12906 (Signed April 11, 1994)
Amended Executive Order 12906 and transferred the power of Executive Order 12906 to the U.S. Department of Homeland Security.
Executive Order 13286 (Signed February 8, 2003)
Troposphere: delays the signal propagation caused by differences in TEMPERATURE, PRESSURE, and HUMIDITY. (maximum error is 1 meter) Ionosphere: delays in the signal propagation caused by free ELECTRONS. (maximum error is 2 to 5 meters) Multipath: lengthening the actual range from the signal transmission path because the signal bounces off of objects (1m) Satellite Clock Error(3-4m): errors in the clocks on board the satellite Orbit Error(2m): errors in the satellite position broadcast by the satellite Geometry of Satellites (mutiplies previous errors): when the satellites have bad angles compared to other satellites
Explain the six sources of errors and how much error it causes
Studies for the system began in 1973 Prototype satellites were launched in 1974 and 1977 Ten NATO countries began participation in 1978 Initial Operational Capability in 1993 Full Operational Capability in 1995
History of GPS
Sound is measured using acoustic devices while light is measured with lasers
How are sound and light used to measure distance?
Basically one more than the # of dimensions
How do we determine the number of points required for trilateration?
As a probability measure # of times the point it is measuring for is within a certain range of where it said it would be (95%)
How is accuracy measured? and what percentage is used?
lasers
How is distance estimated using electromagnetic energy?
Trilateration using four satellite ranges
How is position determined using GPS?
Four points are required. One point causes TRANSLATION that makes the image shift so that the two points coincide. The second point causes ROTATION so that the images orient in the same direction. The third point SCALES the image to ensure it is georeferenced at the correct scale. The fourth because we need one more control point than the number of unknowns.
How many control points are required for georectification, and what is the role of each point? Define each role
spread apart
Should satellites be close together or spread apart to get a good location measurement?
Title
TEXT INFORMATION that immediately establishes MEANING for the map, should be concise and informative and include the data being mapped, also the DATE of the data being mapped
the World Geodetic System of 1984 (WGS84)
What are GPS locations relative to?
Well-Placed control points would be in an equal spread out manner such as a square Poorly-Placed would be close together in no actual organization
What are characteristics of well-placed and poorly-placed control points?
It is very ACCURATE Very SMALL ANTENNAE requirements FREE to the user community Provides GLOBAL COVERAGE Positioning at ANY TIME OF DAY PASSIVE ALL WEATHER operation
What are some advantages and benefits to using GPS?
Space Segment Control Segment User Segment
What are the 3 segments of GPS?
Wide-Area Augmentation System (WAAS): Obtains correction data from satellite broadcast User-Supplied Reference Station: obtains data from second receiver (user responsible) Continuously Operating Reference Stations (CORS): Obtains correction data via internet. Nationwide Differential Correction Data: Obtains correction data from broadcast by ground stations
What are the 4 sources of differential correction data?
1.) Scan the map/photo 2.) Digitize corresponding control points on the scanned image and map projection 3.) Select the best least squares model 4.) Evaluate the root mean squared error (RMSE) statistic. 5.) If the RMSE is unacceptable, re-evaluate control points. 6.) Register the image.
What are the 6 steps in georectifying or georeferencing a map?
Data Model (vector/raster) Data Structure (ESRI shapefile?) Coverage Area (country, state?) Cost and Licensing ($$$?) Themes and Specificity (Vegetation: Deciduous or Coniferous) Source Materials (aerial photography? when? 60s, 90s?) Procurement Time (download via internet? 1 week/6 months?)
What are the 7 considerations when obtaining GIS data?
Projection Author Name Layers Scale Bar North Arrow Legend Creation Date Title Neat Line
What are the MAP ELEMENTS that should be included?
GPS "ENGINE" on a computer card ANTENNAE(built-in or external) DISPLAY (system output) KEYPAD or limited buttons (user input)
What are the components of a GPS receiver?
Receivers and Ground stations
What are the control segments of GPS?
It MONITORS and UPDATES signals, checks the HEALTH and POSITION The master ground station transmits corrections for the satellites EPHEMERIS and CLOCK offsets
What are the ground station control segments of GPS?
Taping Lasers Acoustic
What are the methods used to collect field data?
Geometry of Satellites Orbit Error Multipath Satellite Clock Error Ionosphere Troposphere ******
What are the six sources of error when using GPS? are the causes of error cumulative?
GPS-based solution--slowest but most accurate Network-based solution--faster than GPS-based solution but less accurate Assisted GPS solution (combines GPS and network-based solutions)--Less accurate than GPS-based but more accurate than network-based. (middle ground of speed, accuracy and cost)
What are the three methods to determining cell phone location with respect to 911 and reverse 911 calls? Advantages and disadvantages of each? What kind of error is this?
Single Frequency Receiver and Dual Frequency Receiver SFR: typical hand-held receiver computes position based on the broadcast code (accurate within 3 to 6m) DFR: "mapping" & "survey" grade receivers can estimate ranges based on the phase of the signals carrying the broadcast code. (can eliminate atmospheric effects and be accurate within 3 to 4m)
What are the two receiver types? What is the difference? Advantages and disadvantages of each? Accuracy of each? Which is more accurate? How do they work?
1.) Can be EASILY SEEN on both the image and the map 2.) Is identified on both the image and the map as a VERY SMALL feature (e.g., point, intersection of lines, etc.) 3.) Was ACCURATELY MAPPED on the image and the map
What are three characteristics of GOOD control points (not well-placed)?
Remote Sensing Conversion of Existing Maps (via georectification etc.) Field Data Collection
What are three major approaches to gather GIS data?
Collecting data in the field
What is PRIMARY DATA CAPTURE?
horizontal distance between true north and magnetic north & distance and altitude
What is magnetic declination? What two properties does magnetic North vary over?
Root Mean Squared Error The RMSE is used as an indicator of the accuracy of the spatial analysis and/or remote sensing. The RMSE is a measure of the differences between the predicted or calculated values and the actual, or observed/measured, value.
What is the RMSE? (Root Mean Squared Error)
Distance
What is the range?
1 point = 2D 2 point = 2 1D dot 3 point = one 1D dot
What is the relationship between number of points and dimensions when trilaterating something?
Satellites (30 GPS satellites)
What is the space segment of GPS?
Map Function Map Elements Map Dimensions Map Scale Cartographic Rules Data Visualization Audience
What issues must be considered when making a map?
Trilaterlation
What location measurement method does GPS use to determine location?
Position, Velocity, and Time
What measurements can be determined using GPS technology?
Universal Coordinated Time (UTC)
What time system does GPS use?
Distance: a) Taping--observing the straight-line distance between a starting point along each leg of a traverse. b) Acoustic (sound)-- measured using the known velocity of some energy...(ultrasound) sound waves at a frequency above the limits of human hearing c) Laser: electromagnetic energy travels at the speed of light Angle: Transit and Leveling?
What tools are used to collect angle and distance data? How do they work?
When obtaining GIS data
When must you collect attribute data and its spatial position?
1973
When was GPS created?
US & Nato Countries
Who created GPS?
military and civil communities
Who uses GPS ?
so that the map STANDS ALONE as a communication piece, it should be easy for the audience to read and interpret intuitively.
Why must AUDIENCE be considered when making a map?
types of thematic maps: choropleth, dasymetric, dot density, cartogram, flow, isarhythmic (depending on the data, depends on how the visualization should be presented)
Why must DATA VISUALIZATION be considered when making a map?
so readers can they can interpret it easily and intuitively, these elements include: Layers (appropraite with visual hierarchy) Scale Bar North Arrow Legend Projection Author Name Creation Date Title Neat Line
Why must MAP ELEMENTS be considered when making a map?
maps may be classified based dimensions whether the dimensionality of the values displayed is attributed to point, line, area, or volumetric unites.
Why must map DIMENSIONS be considered when making a map?
maps may be classified based on scale large scale maps have a larger representative fraction than small scale maps.
Why must map SCALE be considered when making a map?
maps may be classified based on function REFERENCE maps are designed to show MUTIPLE general spatial properties or variety of features (ex: highway atlas displays roads, rivers, county and state boundaries, national parks) THEMATIC maps are designed to show the spatial distribution of a SINGLE attribute (ex: nightly weather map showing locations of frontal systems)
Why must the map FUNCTION be considered when making a map?
1.) Figure 2.) Ground 3.) Ground
__________ is the center of the map reader's attention __________ is other useful information but is less important than the figure the __________ appears lower in the visual hierarchy
Scale
a visual or numerical expression of the relationship between ground coordinates and map coordinates
Legend
allows for the map user to TRANSLATE symbols into concepts
Cartographic Rules
color usually symbolizes water, labeling rivers and roads a certain way, or other linear features that may curve or turn
Triangulation
determine position from ANGLES ONLY
Trilateration
determine position from range (or range and an angle)
Least Squares Regression Model (e.g. 1st Order Polynomial)
establishes one-to-one relationship (linear) for all locations in image space (x' and y') and real-world space x' = a + bx(i) + cy(i) y' = d + ex(i) + fy(i)
Map
geographic depiction of real-world features as symbols in their correct spatial location at a reduced scale.
Real-World Space
ground surface on map projection
GPS (Global Positioning System)
is a system for determining precise position in three dimensions based on satellite ranging
Pseudorange
is the distance of the receiver from the satellite
Data Conversion
is the process of converting hard copy mapped geographic data into digital format. common methods include digitzing information from maps or digital imagery. (we digitized that lake)
Primary Data Capture
is the process of recording the geographic position and attributes of features from their NATIVE SOURCE (i.e., not existing maps) common methods are GPS surveying and remote sensing
Link (Link Table)
one location in each corresponding space (image and map)
Author and Creation Date
provides information about the creator and/or data of a map
Value-added Geographic Data
refers to digital geographic data that has been edited to make a more useful dataset
Image Space
scanned map or photo
Symbols: Place Names
should follow a placement and labeling convention
Visual Hierarchy
the ORDER in which map elements are EMPHASIZED based on their appearance to help with map reader to easily interpret the map. most important elements (thematic layers, title, legend) appear highest least important elements (neatline, cartographer name, date, projection) should appear lowest
Leveling
the process of determining the difference in elevation
Georeferencing
the process of relating coordinates in one space to another space (e.g., image space to real world space)
Theodolite used for Transit Leveling
tripod-mounted instrument used for measuring HORIZONTAL angles and VERTICAL angles, contains a telescope and horizontal scale for measuring the direction but also can be rotated along the vertical plane to measure vertical angles directly.
Neat Line
visual frame for the map and acts as a rectangular frame
