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ArcGIS - ESRI, GIS Test one, Geodesy - Week 4 - ESRI Online Course, Geospatial Test 1
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ArcGIS - ESRI, GIS Test one, Geodesy - Week 4 - ESRI Online Course, Geospatial Test 1
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ArcGIS - ESRI, GIS Test one, Geodesy -Week 4 - ESRI Online Course, Geospatial
Test 1
Define geospatial data. - Answers -The data that describes both the LOCATION and
CHARACTERISTICS of spatial features (such as roads, land parcels, and vegetation
stands on the Earth's surface.)
What is GIS? - Answers -Geographic Information Systems is a computer system for
capturing, storing, querying, analyzing and displaying geospatial data.
Define geometries and attributes as the two components of GIS data. - Answers -
Geometric data describe the locations of spatial features, which may be discrete or
continuous.
Attribute data describe the characteristics of spatial features.
Explain the difference between vector data and raster data. - Answers -Vector data use
points and their x-, y-coordinates to represent spatial features of
points, lines, and areas.
Raster data use a grid and grid cells to represent the spatial variation of a feature (such
as elevation or precipitation.)
Vector Data Model: Explain the difference between the georelational data model and
the object-based data model. - Answers -The georelational data model uses a split
system to store spatial data and attribute data.
The object-based data model stores spatial data and attribute data in a single system.
Name two tools or techniques for vector data analysis. - Answers -Tools for vector data
analysis include buffering, overlay, distance measurement, spatial statistics, and map
manipulation.
raster data analysis. - Answers -includes local, neighborhood, zonal, and global
operations.
What is Topology? - Answers -It expresses the spatial relationships between features,
What is TIN? - Answers -Triangulated Irregular Network.
Describe the 3 levels of approximation of the shape and size of the Earth
for GIS applications. - Answers -SPHERE, SPHEROID/ELLIPSOID, GEOID
,What is datum? - Answers -A mathematical model of the Earth, which serves as the
reference base for calculating the geographic coordinates of a location.
Define Projection. - Answers -The process of transforming from a geographic coordinate
system to a projected coordinate system. Can also be reprojected onto another
coordinate system.
Define Relational Database. - Answers -A collection of tables in which tables are
connected by keys.
Define Geographic coordinate system. - Answers -The location reference system for
spatial features on the Earth's surface using latitude and longitude.
Explain the importance of map projection. - Answers -First, a map projection allows us
to use 2 dimensional maps, either paper or digital, instead of a globe. Second, a map
projection allows us to work with plane or projected coordinates rather than longitude
and latitude values. Computations with geographic coordinates are more complex and
yield less accurate distance measurements.
Describe the 4 types of map projections by the preserved property. - Answers -A
Conformal projection preserves local angles and shapes.
An Equivalent projection represents areas in correct relative size.
An Equidistant projection maintains consistency of scale along certain lines.
An Azimuthal projection retains certain
accurate directions.
Describe the 3 types of map projections by the projection or developable surface. -
Answers -A cylindrical projection uses a cylinder as the projection or developable
surface
A conic projection uses a cone
An azimuthal projection uses a plane.
Explain the difference between the standard line and the central line. - Answers -A
standard line refers to the line of tangency between the projection surface and the
reference globe. In other words, there is no projection distortion along a standard line.
The central lines (i.e., the central parallel and meridian) define the center of a map
projection.
How is the scale factor related to the principal scale? - Answers -The scale factor is
defined as the ratio of the local scale to the principal scale. In other words, the scale
factor is the normalized local scale. Will be 1 along the standard line and more distorted
away from the line.
Name two commonly used projected coordinate systems that are based on the
,transverse Mercator projection. - Answers -Universal Transverse Mercator (UTM) grid
system State Plane Coordinate (SPC) system.
Explain how a UTM zone is defined in terms of its central meridian, standard meridian,
and scale factor. - Answers -A UTM zone is mapped onto a secant case transverse
Mercator projection, with a scale factor of 0.9996 at the central meridian. The standard
meridians are 180 kilometers to the east and west of the central meridian.
Explain the UTM coordinate system - Answers -...This system is a specialized
application of the transverse Mercator projection which is both cylindrical and conformal.
It divides the world into 60 numbered zones, both north and south, separated by the
equator. Each zone spans six degrees of longitude and has its own central meridian.
This system was adopted by the US Army Map Service in 1947 for their use in
worldwide mapping and continues to be used worldwide. Florida falls into UTM zones
16 and 17.
When using the UTM system, linear parameters are established. The origin of each
UTM zone is the intersection of its central meridian and the equator, and the parameters
are applied to this origin to make it convenient to work with making all x and y values
positive, or reducing their range. The first parameter is the false easting - a linear value
applied to the origin of the x-coordinates - or the central meridian. The second
parameter is the false northing - a linear value applied to the origin of the y-coordinates
- or the equator. The final parameter used in a UTM grid system is a fixed parameter
called the scale factor. The scale factor is a unitless value (usually less than one) that is
applied to the center point or line of a map projection to reduce the distortion of the
projection in the area of interest. The value of the scale factor for the UTM system is
0.9996
Latitude and Longitude - Answers -Latitude- parallel lines which run east and west and
measure distance north and south of the equator. Longitude- "meridians" which run
north and south and measure distance east and west of the prime meridian.
, A geographic coordinate system.
UTM - Answers -A coordinate system based on the Transverse Mercator projection,
developed in the 1940s. The globe is divided into 60 individual 6-degree wide
longitudinal strips extending from 80S to 84N
The central meridian is assigned a value of 500,00m to avoid negative easting
coordinates. This places the origin outside the zone at 500km west of the central
meridian.
The origin is called a false origin and the easting coordinates are referred to as false
easting
In the Northern hemisphere, the equator is the origin for northing coordinates
, In the Southern hemisphere, the equator is assigned a false northing of 10,000,000m,
again to avoid negative northing coordinates.
Topology advantages and disadvangates - Answers -Topology is concerned with
relationships between spatial objects, but not their physical shape. It is a technique
used to record and manipulate the logical relationships of spatial features.
Advantages.
No duplication. There is no repetition of spatial coordinates between one polygon and
another, so repeated lines are eliminated. This reduces redundancy and improves
integrity of the data.
Error detection and correction. Topology allows for error detection, such as double
digitising, sliver polygons and unclosed polygons. These can all be easily detected
using defined topology
Disadvantages
Some simple operations such as graphic display are slow and cumbersome due to the
complex data structure
Topology requires additional files to store the spatial relationships
AGD66 and GDA94 differences - Answers -GDA94 replaced AGD66 in 2000, thus
moving from a local reference ellipsoid (ANS for AGD66) to a global reference ellipsoid
(GRS80 for GDA94). GDA94 is a geocentric datum and compatible with GPS data.
The Australian Geodetic Datum 1966 (AGD66) is based on the Australian National
Spheroid (ANS) reference ellipsoid with its origin at the Johnston Geodetic Station in the
Northern Territory. This datum was designed to be a best fit for the Australian region.
The centre of the ANS does not coincide with the centre of the Earth but lies about
200m from it.
Vector analysis operations - Answers -measurement
queries
buffering
reclassification
overlay operations
Raster analysis operations - Answers -neighbourhood functions
reclassification
overlay
central meridian - Answers -A central meridian is a meridian that passes through the
center of a projection. The central meridian is often a straight line that is an axis of
symmetry of the projection.
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