Locating data in space correct answers spatial referencing system
2 ways of dealing with unflat earth surfaces in map format. correct answers 1. Geographic coordinate systems locate data on spherical level (la/long)
2. Projected coordinate systems locate data to a flat surface (metres)
Datum...
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Locating data in space correct answers spatial referencing system
2 ways of dealing with unflat earth surfaces in map format. correct answers 1. Geographic
coordinate systems locate data on spherical level (la/long)
2. Projected coordinate systems locate data to a flat surface (metres)
Datum correct answers Mathematical model that describes the shape of the earth. different
datums for different parts of the earth based on different measurements
The earth is an... correct answers elipsoid
shape of the earth is further skewed by correct answers the influence of the continents
Geographic coordinate system correct answers derived by a datum, defines location's using a 3D
spherical surface, a feature is referenced by its longitude and latitude values, measured in
decimal degrees or in deg, min and seconds, latitudes measured relative to the equator,
longitudes measured relative to the prime meridian.
Problems with GCS 1 correct answers Latitude and longitude are not uniform units of
measurements and vary by location, therefore unable to measure distances, areas or direction
between two points.
Problems with GCS 2 correct answers Earth isn't round, actually a lumpy spheroid, thus the
south pole is closer to the equator than the north pole. This means there are many different GCS
depending on the datums used
Projections correct answers used to portray all or part of the spherical earth on a flat surface, data
is projected from GCS, every set has own set of advantages and disadvantages, select one with
reduced distortion of most important features.
three main types of projections correct answers 1. Cylindrical
2. Conic
3.Azimuthal (planar)
Cylindrical projection, Mercator correct answers projected on a cylinder tangent to the equator
(Normal)
Features of the Mercator (cylindrical) correct answers distances: are true only along the equator
but reasonably correct with 15 degrees of the equator.
areas and shapes: large areas are distorted
Distortion: increases away from the equator and is extreme in polar regions. map is not
perspective, equal area or equidistant.
, Cylindrical, transverse Mercator correct answers Projected on cylinder tangent to a chosen
meridian
transverse mercator correct answers Distance: are true only along the central meridian selected
by the map maker or else along two lines parallel to it.
all distances, directions, shapes and areas are reasonably accurate within 15 degrees of the
meridian.
distortion: of distances, directions and sizes of areas increase rapidly outside of the 15 degree
band.
Lambert conformal conic correct answers projected on a cone tangent at two standards parallels
Lambert conformal conic correct answers Often used to show a country or region that is mainly
east west in extent.
Distances: true only a along standard parallels; reasonably accurate elsewhere in limited regions.
Directions: reasonably accurate
Distortion: of shapes and areas minimal but increases away from standard parallels.
Orthographic, Azimuthal correct answers Geometrically projected into a plane. point of
projection is at infinity
Orthographic correct answers Use for perspective views of the Earth, Moon etc.
Directions: are truly only from centre point projection.
Scale: decreases along all lines radiating from centre point of projection.
Areas and shapes: are distorted by perspective; distortion increases away from centre point.
Australian datums and grid references correct answers AMG66, AGD84, GDA94, GDA
Adoption?
deciding on a coordinate system correct answers depends on:
where you are located, orientation of study area, size of your study area, amount of quantitative
analysis needed, extensions that only operate on projected data, is your other data in a different
format, what do your colleagues or organisation use, suitable for purposes and consistent
between layers.
Data types.
Three types of vector
two types of tables
raster correct answers -shape file, coverage and feature class.
-dBASE and Excel
- Grid
Mapfile correct answers displaying data in ArcMap, doesn't contain spatial data, refers to data
describes its arrangement, colouring, symbology etc in a map.
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