ESF 300- Exam 1
The 1980s GIS was significantly altered by
- (1) the PC and - (2) the workstation - new GIS software could better exploit more advanced hardware
Manual map overlay as a method was first described comprehensively by:
- Jacqueline Tyrwhitt (1950) Town and Country Planning - Ian McHarg (1969) used blacked out transparent overlays for site selection in Design with Nature
latitude
- Lines of Parallel (never touch) Range of 0-90o (N and S, 0 at equator, 90o at pole) - Lines of latitude get shorter and shorter from equator to pole - Software generally considers northern latitudes as positive and southern latitudes as negative - Sphere: Angle measured from center of the earth to points north or south of equator - Ellipsoid: Angle between the equatorial plane and a line normal to the reference ellipsoid
longitude
- Meridians (distances between them not constant) ◦ - Range of 0-180o (E and W; 0 at prime meridian) ◦ - Software generally considers western longitudes negative and eastern longitudes positive - Angle measured from the center of the earth to the east or west of the prime meridian (sphere) ◦ - Angle between reference plane and plane passing through the point: both planes perpendicular to the equatorial plane
geoid
- The geoid is defined as the surface of the earth's gravity field, which approximates mean sea level. - It is perpendicular to the direction of gravity pull. - Influenced by gravity and rotation only - no wind or tides - Since the mass of the Earth is not uniform at all points, the magnitude of gravity varies, and the shape of the geoid is irregular - Plumb lines will always point directly perpendicular - Water surface always parallel - It is the actual physical shape of the Earth - - GRACE Video (Gravity Recovery and Climate Experiment)
raster cell model
- Uses a Row and Column grid format. - One grid cell is one unit or holds one attribute. - Every cell has a value, even if it is "missing." - A cell can hold a number or an index value standing for an attribute. - A cell has a resolution, given as the cell size in ground units.
2 coordinate systems
- geographic - projected
ellipsoid
- now used interchangably with spheroid - Defined equatorial and polar radii - Earth shape over smppthed and average sea-surface - Best models represent the earth shape to within about 100 meters - Geoid- the surface of gravity's force on the Earth
coordinate system issues to consider
- region of analysis - level of analysis required - level of accuracy required
earth models characteristics
- shape of eaarth - size of earth - environment of earth - constantly changing
GIS origins
- thematic cartography - dr. john snow
what do we use GIS for?
- to visualize and communicate - answer questions
representative fraction scale
1 unit measured is 24,000 units on the ground 1 inch on the map = 24,000 inches in the real world. 1 cm on the map = 24,000 cm in the real world Be care with unit conversion in RF 1" = 24,000" = 2,000' 1cm = 24,000cm = 240m
universal transverse mercador zones
2 dimensional (horizontal) coordinate system UTM zone #'s designate 6º wide longitudinal strips extending from 80º S to 84º N latitudes Each zone has CM- not 0
How many more cells would a raster data set require if the cells were reduced in size from 30 m on the side to 10 m on the side?
9x as many
What is a GIS?
A GIS is a computer information system to aid in the collection, maintenance, storage, analysis, output and distribution of spatial data and Information - GIS is a tool box - GIS is an approach to science - GIS is a multi-billion dollar business.
What is the difference between a grid and a graticule?
A grid is a network of lines used to identify x and y coordinates on a map, while graticules are lines showing parallels of latitude and meridians of longitude for the earth.
topology
A set of rules that define the relationships between spatial features. is a model by which entities (points, lines/arcs, polygons) are "self aware" of their surroundings • Features are stored with information about related or adjoining features • Rules establish what is spatially acceptable and what is not spatially acceptable.
map projections
A transformation of the spherical or ellipsoidal earth onto a flat map is called a map projection. The map projection can be onto a flat surface or a surface that can be made flat by cutting, such as a cylinder or a cone.
point
A zero dimensional position, representing the location of a solitary feature • The feature may have many associated attributes (e.g., species and DBH of a tree), the point denotes where this feature is only
polygon
An entity that encompasses an area • A single line that the ending point connects to the starting point • Multiple connected lines that close back on the beginning point • Adjacent polygons typically share the edge or common
digitizing
Captures map data by tracing lines from a map by hand Uses a cursor and an electronically-sensitive tablet Result is a string of points with (x, y) values
transverse mercador
Central meridian- the point at which a cylinder is "touching" the earth in a transverse mercator CM= point of no distortion Distortion increases as distance W or E of the CM increases.
field
Collection of spatial distributions of a phenomena.
What does the acronym COGO stand for?
Coordinate Geometry
mercador projection
Cylindrical projection of earth ↑ Equator- the point at which a cylinder is "touching" the earth Distortion increases as distances N to S from the equator increases.
what can be done about file size?
Data compression! Little difference in quality but drastic change in size
geocoding methods
Digitizing Scanning Field data collection Address matching
state plane coordinate systems
Each state has its own zone Projection used for each state is also variable States that are elongated from E to W generally usa lambert conformal conic projection
georeferencing
Georeferencing is simply associating things with a physical place
who created spatial data model?
George EP box All models are wrong but some are useful ." "Remember that all models are wrong ; the practical question is how wrong do they have to be to not be useful? .
What is the difference between heads-up digitizing and hardcopy digitizing?
Heads-up digitizing involves using digital images of input maps as a backdrop on a computer screen, while hardcopy digitizing involves using paper maps on a digitizing table.
conformal v. equivalent maps
No flat map can be both equivalent and conformal. Conformal - Shapes on the map "conform" to reality Equivalent - Feature area is preserved
mixed pixel problem
RULE: winner takes all If majority of cell is water, then the cell becomes water
line
Represent linear features (1D) •Can comprise multiple short line segments separated by Vertices and begin and end with Nodes. • Attributes can be assoc. with the entire line or any line seg., vertex or node on the line
datum
Something used as a basis for calculating or measuring.
lambert conformal conic
Standard parallels- the point at which a cone is touching the earth in a conic projection sp= point of no distortion Distortion increases as distance N to S from the SP increases Greater total distortion in south
coordinate geometry (COGO)
Surveying data Traverses (Open or Closed) connected set of points from known starting point list of directions (bearings/azimuths) and distances (lengths) Use basic trigonometric functions to convert to X,Y coordinates
magnetic declination
The magnetic north shifts slightly each year so the Magnetic north and geographic north aren't the same. Eventually, there can be a polar shift possibly.
attribute data
The stuff that makes the pretty pictures more useful • Both logical and physical data models have evolved over time. • DBMSs use many different methods to store and manage flat files in physical files. - Much more about this in a couple of weeks Attribute data are stored logically in flat files i.e., a matrix of Rows and Columns.
cartesian/planar/rectangular coordinates
Use coordinate pairs or triples (3D) to represent positions on a flat map Projecting something spherical onto sm flat.
-oid
a suffix meaning resembling or like, used in formation of nouns and implying incomplete or imperfect resemblance
spheroid
an imperfect sphere- all points not equidistant to center- thats really us
computer numbers work with ____________ numbers
binary digits - 1 - 0
"In vector data models, which of the following shapes are NOT used as elements to represent real world entities?"
cells
4 map types
choropleth isopleth feature dot density
reduce mixed pixels by
decreasing cell size
object
discrete, identifiable unit
"In vector data models, topology is used to:"
enforce connectivity and adjacency
Vector data models usually have a simpler data structure than raster data models
false
Vector data models usually require more computer storage space than raster data models
false
easting origin
for each zone is always placed an arbitrary # of feet west of the western boundary of the zone False easting- the # of feet added in the western edge coordinates to keep values positive
geocoding
is the conversion of spatial information into digital form
"The location of a cell in a raster data set is based on cell row and column number, cell size, and known coordinates of the:"
lower left cell
"In vector data models, starting and ending points for a line are referred to as:"
nodes
types of RS systems
passive - cameras - orbiting satellites active - radar - sonar
northing origins
placed at an arbitrary # of feet south of the state border False northing- the # of feet added in the southern edge coordinate to keep values positive
geodesy
science of measuring earth
Analysis is usually more complex with vector data than with raster data
true
Raster data models are better than vector data models for representing phenomena that change frequently across space.
true
shapefile
• Nontopological data structure •No implicitly stored adjacency information • Simple • "Good enough" for our purposes
why is topology good
•used in enterprises and large projects • high data accuracy • greater data integrity
