GIS Midterm
How can angular units be represented?
(1) Degrees Minutes Seconds (DMS) - example: 29^degrees 53' 07" N (2) Decimal Degrees (DD) - example: + 29.0304
Describe the steps (pyramid) of mapping.
(1) Earth --> (2) Ellipsoid --> (3) Datum --> (4) Geographic Coordinate System (GCS) --> (5) Projected Coordinate System (PCS)
List some conic type projection examples and their pattern of distortion.
(1) Equidistant Conic and (2) Albers Equal Area Conic pattern of distortion: for tangent - standard parallel; for secant - standard parallelS
List some azimuthal type projection examples and their pattern of distortion.
(1) Gnomi, (2) Azimuthal Equidistant pattern of distortion: for tangent - standard point; for secant - standard parallel
List some cylindrical type projection examples and their pattern of distortion.
(1) Mercator and (2) Cylindrical Equal Area pattern of distortion: for tangent - standard parallel; for secant - standard parallelS
What are some examples of local datums?
(1) North American Datum 1927 (NAD27) (2) North American Datum 1983 (NAD83)
Describe the GIS Process.
(1) Physical World (i.e. determine subject) (2) Define Protocols (i.e. determine audience and what story to tell) (3) Collect & Edit Data (4) Analyze (5) Report Results (6) Decide & Act
What are some examples of geocentric datums?
(1) World Geodetic System 1984 (WGS84)
In what ways can projections be distorted?
(1) area (size), (2) shape, (3) distance, and (4) direction
GIS is an interdisciplinary subject combining __________ and _________.
(1) computers, (2) geography
List the types of map projections.
(1) cylindrical, (2) conic, (3) azimuthal (planar)
Map data falls into which two categories?
(1) discrete, and (2) continuous
List the types of datums.
(1) local datums and (2) geocentric datums
Which attribute (non-spatial) data measurement levels present categorical information?
(1) nominal and (2) ordinal
List the attribute (non-spatial) data measurement levels.
(1) nominal, (2) ordinal, (3) interval, and (4) ratio
What are the three aspects that each projection type can be positioned over the globe by?
(1) normal (2) transverse (3) oblique
Location only makes _________ when compared to _________________________________.
(1) sense; (2) some frame of reference
List Earth models in GIS.
(1) sphere, (2) ellipsoid, and (3) geoid
What are the components of datums?
(1) spheroid, (2) origin, (3) azimuth from origin to a second point, and (4) orientation of the ellipsoid to the geoid Note (in case you forgot like me): The vector from an observer (origin) to a point of interest is projected perpendicularly onto a reference plane; the angle between the projected vector and a reference vector on the reference plane is called the azimuth.
Geographically spatial data are typically represented by which two main data models?
(1) vector, and (2) raster
Which attribute (non-spatial) data measurement levels present quantitative information?
(3) interval and (4) ratio
List other map projection types.
- Cube - Fuller - Bonne Pseudoconic - Polyconic - Equirectangular - Polar Stereographic - Robinson
What were some of the first commercial softwares?
- Mapguide (Autodesk) - PowerMap (Bentley Systems) - Geomedia (Intergraph) - Smallworld (GE) - ArcGIS present
What are the disadvantages of globes?
- have small scales providing little detail of the earth - Globes are expensive and inconvenient to carry - have limited view of the earth
Describe azimuthal type projection.
- preserves area and direction - is polar region oriented examples: Gnomi, Azimuthal Equidistant
Describe conic type projection.
- preserves area or distance - is E/W oriented examples: Equidistant Conic, Albers Equal Area Conic
Describe cylindrical type projection.
- preserves shape and distance - is N/S oriented examples: Mercator, Cylindrical Equal Area
Why do we use Projected Coordinate Systems (PCS) instead of the Geographic Coordinate System (GCS)?
- provides more holistic view of entire earth - easy to comprehend - units are linear (m, ft, etc.) - easy to estimate size and distance
How many conversions between raster and vector data are considered okay?
1-2; more than 2 produces too many errors
When did GIS become commercialized?
1981 with ESRI creating Arc/Info GIS
What GIS are we currently using at USF?
ArcGIS Desktop
Although USA is now considered the leader in GIS, which country was first?
Canada
T/F: In both theory and GIS practice ordinal and nominal data measurement levels are different.
FALSE: In GIS practice, ordinal and nominal data measurement levels are the SAME
T/F: In both theory and GIS practice interval and ratio data measurement levels are different.
FALSE: in GIS practice interval and ratio data measurement levels are the SAME
T/F: Pixels can present more than one attribute.
FALSE: pixels can only represent ONE attribute
T/F: A feature class can contain more than one type of geometry/feature/object?
FALSE; a feature class can only contain ONE type of geometry/feature/object in GIS
How is the Geographic Coordinate System (GCS) different from datums?
GCS uses units (degrees lat and long)
What are the pros and cons of the vector data model?
PROS: (1) stores features with high degree of precision and detail (2) great flexibility in the number/type of attributes - can store hundreds (3) compact in terms of space needed for storage (4) suited for specific types of analysis CONS: (1) poorly adapted for storing continuous data (2) calculating derived information (i.e. slope, direction) is difficult (3) not suited for other types of analysis
What are the pros and cons of the raster data model?
PROS: (1) suited to storing continuous data (2) analysis is often simple and rapid in performance (3) more extensive set of analysis tools than in vector data model CONS: (1) not as precise (2) needs greater storage space (3) can only store one numeric attribute per cell
How can you prevent distortion of your map?
Properties: ● Preserve Area = Equal Area ● Preserve Distance = Equidistant ● Preserve Direction = Conformal/Azimuthal ● Preserve Shape (angles) = Conformal Orientation: ● Preserve E-W orientation = Lambert Conformal Conic ● Preserve N-S orientation = Transverse Mercator ● preserve neither orientation = Oblique Mercator
T/F: All map projections introduce distortion.
TRUE: all map projections introduce distortion - type and degree of distortion varies with map projection - choice of map projection comes with comparing distortions and choosing most suitable distortion
T/F: You can convert vector data into raster data.
TRUE: you can convert vector data into raster data
Describe the history of GIS.
The Early Years (1960-1980) The Specialized Years (1980-2000) GIS Today Share & Collaborate (2000 - present)
When was the term "GIS" defined?
The Open Geospatial Consortium (OGS) - founded in 1994
Describe the World Geodetic System 1984 (WGS84).
Type of Datum: geocentric Ellipsoid Based On: Geodetic Reference System 1980 (GRS80) Computed: through Doppler satellite measurements (starting point origin of Earth) - official datum of US Department of Defense - Global Positioning Systems (GPS) are based on WGS84) - datums see updates/adjustment multiple times (every few years)
Describe the North American Datum 1927 (NAD27).
Type of Datum: local Ellipsoid Based On: Clarke 1866 Computed: manually via triangulation with single point in Meades Ranch, Kansas (because center of USA) - more accurate for USA - consists of 25,000 points
Describe the North American Datum 1983 (NAD83).
Type of Datum: local Ellipsoid Based On: Geodetic Reference System 1980 (GRS80) Computed: with remote sensing satellite technology - official datum of US, used by federal gov't - more accurate than NAD27 due to advancing technologies (only slightly off origin of Earth) - more accurate for US - consists of 300,000 points
Describe the State Plane Coordinate System (SPCS).
Type of Projection: - N/S for 31 states= transverse cylindrical (Universal Transverse Mercator (UTM)) - E/W for 28 states = secant conic (Lambert Conformal Conic) - some states have both systems (including FL, Alaska) - 124 zones total - unique for each state
Describe the Lambert Conformal Conic.
Type of Projection: secant conic Distortion: two standard parallels Orientation: E/W - Used on many USGS maps (since '57) - Best for maps of areas within one zone
Describe the Universal Transverse Mercator (UTM).
Type of Projection: secant transverse cylindrical - uses Mercator projection on each region to compile into UTM Orientation: N/S - zones are six degrees wide and numbered 1-60 from the International Date Line (180 degrees W) - zones are identified by their position N and S of equator
What is a geocentric datum?
a datum that optimizes the fit for the entire earth
What is a local datum?
a datum that optimizes the shift for the best fit at a particular location
Define ellipsoid in relation to GIS.
a mathematical model that approx. the earth -regular shape - used in GIS - contains: spheroid, semi-major axis, semi-minor axis that differs in each model examples: Clarke 1866, Geodetic Reference System 1980 (GRS80)
Define geoid in relation to GIS.
a model of the earth that takes gravitational force into account, displaying the surface of the earth's gravitational field (approx. same as mean sea level) - irregular shape - most accurate model - model changes every minute due to gravitational force
Number of conversions between raster and vector data is inversely proportional to ___________.
accuracy
Define Geographic Information System (GIS).
an information system used to manipulate, summarize, query, edit, and visualize spatial and non-spatial information stored in a computer database
What units does the Geographic Coordinate System (GCS) use?
angular units: x = longitude y = latitude example: (lat, long)
When did GIS become open source (free use)?
around 1994 with GRASS (open source program)
Define the relationship between attributes and spatial data.
attributes contain information not related to geography/location about data related to geography/location - simplified definition: attributes contain non-spatial data related to spatial data example: name correlated to lat/long, population correlated to area
Define Geographic Coordinate System (GCS).
based on spherical globe coordinates; represented by degrees of latitude and longitude (3D) - alternatively called: Globes/Spherical coordinates
Why is the raster data model better suited to store continuous data?
because each pixel can have a value completely different from its neighbors
Describe the ordinal data measurement level.
categorical/qualitative info WITH the ability to compare - differentiates on the comparative or ranking relationship example: city size: small, med, large
Describe the nominal data measurement level.
categorical/qualitative info WITHOUT the ability to compare - names or categorizes with no implication that one subgroup is more or less important than another - cannot perform mathematical operation between data example: name of county
When you want to display more attributes, what type of map expands the number of attributes that can be displayed on a map?
chart map
Who was Howard Fisher?
created first computer mapping software (SYMAP)
Define non-spatial data (attributes).
data not related to geography/location example: type of building
Define spatial data.
data related to geography/location example: longitude/latitude
Define raster data model.
designed to store continuous data - simpler structure than vector data model - set of spatial data is represented using a series of small squares (called cells or pixels) - pixels contain numeric code indicating a single attribute - raster data model is stored as an array of numbers that make up a grid of cells one basic raster feature: (1) pixels
Define vector data model.
designed to store discrete data - uses a series of x-y locations to store information - geometry based - organized into polygons and nodes three basic vector features/objects/geometries: (1) points (0D), (2) polylines (1D), (3) polygons/areas (2D) -features represented using one or more x-y coordinate locations - type of feature/object used in vector model depends on scale of map
Describe normal aspect of a projection.
developable surface parallel with the equator
When did GIS generally "begin"?
early 1960s
In GIS, features are grouped into data sets called ______________________.
feature classes
Who was Jack Dangermond?
founder of ESRI (with his wife Laura!)
Numeric data classes for polygons are usually portrayed by what type of map?
graduated color map, or a choropleth map
Point or line data are usually portrayed by what type of map?
graduated or proportional symbol map
What does it mean to have a tangent or secant case in map projection?
it is how the map projection surface interacts with the globe - zero distortion where interaction occurs - increasing distortion with increasing distance away from place of interaction
What are some questions that GIS can answer?
location, pattern, condition, trends, and modeling questions
Describe the difference between longitude and latitude.
longitude (meridians): vertical lines going North to South - remember: long-dong latitude (parallels): horizontal lines going West to East - remember: lat-fat
Define a Projected Coordinate System (PCS).
map projection of a coordinate system - converts spherical coordinates to planar - transforms 3D coordinates to 2D coordinates
Define discrete data.
objects in the real world with specific locations or boundaries - values change abruptly from one category to another example: cities, roads, or soils units
Resolution is defined by what in raster data?
pixels' x and y dimensions
Describe the ratio data measurement level.
quantitative info that provides meaningful differences WITH meaningful zero - can multiply/divide example: population density, height, weight
Describe the interval data measurement level.
quantitative info that provides meaningful differences WITHOUT meaningful zero - between values of phenomena - on a standardized scale - cannot multiply/divide example: temperature, elevation
Define continuous data.
represents a quantity or variable that is measured and recorded everywhere over a surface - values continuously change; no abrupt or distinct boundaries example: temperature, elevation
Describe lines in the vector data model.
represents objects in one dimension - includes two or more pairs of coordinates (starting/ending points are called nodes, intermediate points are called vertices) properties: locations, length example: roads
Describe polygons/areas in the vector data model.
represents objects in two dimensions (a group of vertices that define a closed area) -starting/ending points are the same point properties: position, perimeter (length), area example: state
Describe points in the vector data model.
represents objects that have no dimensions - most basic element in vector data model properties: x,y coordinates example: location of outhouses
Describe pixels in the raster data model.
represents spatial data in small squares that correlate to numeric code indicating a SINGLE attribute - images not as clear when using pixels - pixels are color coded - pixels can be integers or decimals properties: position in the array (i.e. row= 3, col = 4) in relation to x-y coordinate example: temperature, elevation
Cell size is inversely proportional to ____________.
resolution's level of preciseness
Describe secant cases in map projection.
secant case: map projection surface interacts by intersecting the ellipsoid - produces standard parallels (TWO) or two standard lines - no distortion along standard parallels/two standard lines - error increases with distance away from standard parallels or lines
Define datum.
set of reference points from which spatial measurements are made - used to position the ellipsoid to the earth's surface - minimizes the discrepancy between geoid and ellipsoid - used to shift the ellipsoid relative to the geoid to achieve best fit between the two
Describe tangent cases in map projection.
tangent case: map projection surface interacts by touching the ellipsoid at a single point or line - produces a single standard parallel or point (SINGLE) - no distortion along standard parallel or point - errors increase with distance away from line/point of touch (standard parallel or point)
Who was Robert Tomlinson?
the "Father of GIS"; developed Canada Geographic Information System; first computerized GIS (1963)
Define coordinate system.
the choice of which type of values and units to store the x-y data set in - combination of a Geographic Coordinate System (GCS) and a Projected Coordinate System (PCS)
Define sphere in relation to GIS.
the old, original model of Earth
What is the aspect of a projection?
the orientation of the developable surface relative to the globe
What is map projection?
the process of representing the curved 3D surface of the earth on a flat 2D surface
What does the State Plane Coordinate System look like in Florida?
three zones: (1) East, (2) West, (3) North ● East Zone = Transverse Mercator ● West Zone = Transverse Mercator ● North Zone = Lambert Conformal Conic
List some GIS web solutions.
○ ArcGIS Online ○ Google Earth ○ Google and Bing maps ○ Web mapping (story maps, etc.)
List the file formats used to store the raster data model.
○ Esri GRID ○ GeoTIF ○ GIF ○ PNG ○ JPEG
