Why can getting points from a GPS into ArcGIS be problematic?
Poor connection - hardware and software issues; different
companies/products/versions
Difficult to find the specified datum/projection
What is remote sensing? Give examples.
Collecting information from a distance; ex. photo...
GIS Exam Questions and Answers
2024/2025
Why can getting points from a GPS into ArcGIS be problematic?
Poor connection - hardware and software issues; different
companies/products/versions
Difficult to find the specified datum/projection
What is remote sensing? Give examples.
Collecting information from a distance; ex. photographs or radar/LiDAR. Typically
satellite or air plane. Offer great detail over a continuous surface
How is remote sensing imagery stored?
Great detail = large file sizes. Stored using raster data models - typically, three
rasters superimposed together to get color (one each for Red, Green, and Blue value:
RGB)
How can we pull information from remote sensing?
Can often be detected by the human eye and then digitized or classified based on
type; but is very time consuming and expensive. Plus, humans can make mistakes. So
we increasingly use computers to pull out the information correctly. Computers use
automatic processing, being trained to write rules to automatically pull out information.
This is hugely beneficial for large datasets. Not ideal for small areas.
What is artificial intelligence?
Show computer what to look for and it figures it out; E.g. cancer on a brain scan,
gentrification on street view. Cutting edge of computer technology - but humans are
unsure of how it actually works. Computer is literally thinking for itself (training itself).
Huge potential moving forward - perhaps someday replace all humans
Light Detection and Ranging - similar to SONAR, but uses laser rather than sound
waves. Device sends out a laser pulse, and records how long it takes for it to bounce
off surface and return to detector. Benefits: Highly Accurate; can penetrate foliage
How are drones used in RS and what is their benefit
Similar to RS from air photos or satellite. However, much cheaper to collect the
information and can be collected by user at will, rather than relying on someone else's
satellite.
How can smart phones be used for data collection?
Because they are hugely powerful data collection devices, with a large number of
sensors (accelerometer, GPS, gyroscope, microphone, barometer, thermometer). Have
lots of storage for data, cloud connections, and high processing speed. The fact that
our phones are constantly collecting data about us creates massive privacy issues.
Define projections and coordinates.
Projections compensate for the earth being spherical but being represented on a flat
surface (map)
Coordinates allow us to accurately and reproducibly locate features on the earth's surface
Define geodesy
Science of measuring the shape of the earth - humans have been refining the model
for thousands of years
Describe earth's shape.
Earth is an Ellipsoid, not a perfect sphere. Two radii:
•r1, along semi-major (through Equator)
•r2, along semi-minor (through poles). More specifically, its shape is a geoid, because it is
rough, not smooth, due to differences in internal gravitational pull. This causes some areas to
A model of the earth's size/shape (ie a model of the Geoid). Applied to a specific
origin/reference point. Different datums created for places around the world.
Continually refined over time (ex: NAD 27 vs 83). Not much change in recent decades.
Horizontal and Vertical datums exist
With projections, is there more distortion on small scale or large scale maps?
Small scale maps
Projections typically only maintain 1 or 2 of what following features, and must distort at least
one feature?
Area, shape, distances, and angles
Define spherical coordinates.
Use the length of a vector originating at the ellipsoid center to define the location on
the surface
Define latitude and longitude.
Latitude: Lines running parallel east to west; Equator is the baseline
Longitude: Lines running from pole to pole; Meridians; Greenwich (Prime) Meridian is the
Divides the world into 60 zones (including North and South). Each zone has an origin
based on False Easting/Northing
Describe the relationship between GIS, coordinate systems, datum and projections and what
happens in GIS when they differ.
Each layer has a coordinate system, and datum (usually projection) - even if it is not
defined. All layers on the map must be in the same system to allow them to line up
(superimpose). Thus, GIS projects on the fly to one system for all of the different
layers. Data frame has one projection/coordinate system which is defined by first file
added. All others that differ are re-projected on the fly to match this one.
What is the name of the file that contains projection information?
PRJ
How can you see the projection information for the layer? For the data frame?
Layer: go to properties >> source
Data frame: go to properties >> coordinate system
How can projections cause issues?
•Often the projection/coordinate/datum information is missing or incorrect
•E.g. bringing in GPS data
•If information is wrong/not specified, major problems for your data
•Will be plotted in the wrong location
•Often just float out in space
•Will not line up between the layers
•Warning Message for Geographic Coordinate Systems not Aligning
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