Geographic Information Systems
Connects spatial data and list data to answer geographical questions and solve geographical problems
Spatial Data
Coordinate system
4 common spatial relationships
Distance, intersection, adjacency, containment
Common uses of GIS
Visualization, spatial modeling, social science and policy, planning and infrastructure, natural sciences, information technology
Discrete
Has clear boundaries
Examples of discrete
States, cities, countries, bodies of water
Continuous
Has no clear boundaries (except the edge of the data)
Data Model
How we encode a geographic phenomenon, be it discrete or continuous into a digital data on a computer
Vector
Points, lines or polygons defined by x, y coordinates (lat/longs) and an attribute table
Discrete
Vector data tends to be stored as
Example of vector
Political boundaries, building sites, roads, train lines
Raster
A grid of cells with values
Continuous
Raster data tends to be stored as
Example of raster
Satellite/aerial imagery, elevation
Geographic knowledges
More fundamental than maps, GIS, or even writing
Developmental and cognitive psychology
Humans have the (apparently unique) ability to think about geography abstractly
Cultural social processes
How people understand geography varies across different places and times
There are multiple kinds of legitimate geographic knowledge
Map
A graphic representation of the environment
A geographical proposition/argument
Visual, abstract, geographic practice
Reference map
Involve multiple topics or themes and no one theme is most prominent
Thematic maps
Focus on one theme
Any of a huge variety of specific themes
Icons
The shape of Texas is an example of
Latitude
Parallel lines also known as y
Longitude
Meridian lines also known as x
Sexagesimal system
Of or related to 60
Degrees, minutes, seconds
N 40° 46’ 7”, W 73° 58’ 11”
Converting DMS to DD
A) Degrees become the whole number
B) Calculate the total number of seconds (minutes * 60 + seconds)
C) Divide by the possible number of seconds (# from B/3600)
D) Add to the whole number
Converting DD to DMS
A) Degrees become the whole number
B) Multiply the decimal by 60 (decimal * 60)
C) Multiply the remaining decimals by 60
Negative
Are South and West negative or positive?
Positive
Are North and East negative or positive?
Global Navigation Satellite Systems
Space-based global navigation system that in which a receiver unit calculates its location and time
Satellites emit radio signals. A receiver takes the signals from multiple satellites to calculate the receiver’s location
GPS receiver unit
The device that gathers GPS satellite signals and uses them to calculate your location
Fix
An accurately defined location identified with a GPS unit
Waypoint
A recorded GPS fix that is part of a series
24 satellites
Global navigation systems require at least _________ for full world-wide coverage.
Space, control and user segment
Name the 3 GPS parts
How GPS works
Satellites broadcast current time and location. They are synchronized
GPS receiver gets the signal and records the time delay between when the signal was sent vs the time the receiver got the message; indicating the time
Uses space trilateration to calculate its location on time delays
Space trilateration
A method for determining positions using the geometry of sphere in 3 dimensions
4
Trilateriation uses known locations of at least ___ GPS satellites
Reasons for errors in GPS
GPS are weak
GPS chips break
If you drop your phone or have an old one
Relativity
Clock bias
Number of visible satellites
Dilution of precision
Systematic bias
Can anticipate this and reduce it
Random bias
Impossible to eliminate
GPS Augmentation
Using external information to improve the accuracy of GPS readings
Differential GPS
Can be as good as 1 to 5 meters
Uses two GPS receivers
One at a base station
A second moving about in a field
Spatial phenomena
Continuous geographic phenomena
Discrete geographic phenomena
Stored digitally in raster and vector datasets
Non-spatial phenomena
Categories of data measurement
Nominal
Ordinal
Interval
Ratio
Stored digitally in attribute data
Nominal
Named types
Ordinal
Hierarchy of types
Interval
Measured difference between types based on an arbitrary zero point
Ratio
Measured difference between types based on an absolute, known zero point
Raster data
Only one corner of the grid has a latitude and longitude (the origin: usually the upper left)
Cells are regularly sized with no gaps
Latitude and longitude is not stored for each cell
Resolution
The geographic size of a cell on the ground
Node
Beginning points and ending points
Lines: beginning and ending are different
Polygons: beginning and ending are the same
Vertex
Connecting points in the middle
Arc/segment
Line connecting points
Triangular irregular network
X, y, z values
Network of points defining triangles
Best for continuous data
ESRI
Originally Environmental Systems Research Institute, replaced by ArcMap
Feature class
A single set of GIS data is called this. Appears as layers in the contents of Arc GIS.
Simple
Raster data storage is
Complex
Vector data storage is
Shapefile
Stores 1 feature class
Geodatabase
Can store multiple feature classes and other stuff