Midterm Flashcards
Cloud Computing
Data and software that in the past
has been stored on desktop computers
is now stored “in the cloud” thanks to wireless networking/higher speeds
Service-Oriented Architecture (SOA)
Service providers (server) and service consumers (clients) that communicate with each other
Geographic Approach
Step 1: Ask–“framing the question from a location-based
perspective”
– Step 2: Acquire–determine what data are needed
– Step 3: Examine—examine and evaluate the data
– Step 4: Analyze—process and analyze the data
– Step 5: Act—present the results
Georeferenced or registered layers
layers are all in the same
map projection, datum, and
coordinate-system
3 families of projections
1) Cylindrical
2) Conic
3) Planar/Azimuthal
Distortion ___ as the size of the geographic area that you
are working with _____.
increases, increases
Albers equal area/conical
equal area; conformal along standard parallels
uses: small regional and national maps
Azimuth equidistant/planar
equidistant: true directions from map center
uses: air and sea navigation charts; equatorial and polar area large-scale maps
Equidistant conic/conical
equidistant along standard parallel and central meridian
uses: region mapping of midlatitude areas with east-west extent; atlas maps for small countries
Lambert conformal conic/conical
conformal; true local directions
uses: navigation charts, U.S. State Plan Coordinate System for all east-west State Plane Zones; continental U.S. maps; Canadian maps
Mercator/cylindrical
conformal; true direction
uses: navigation charts, conformal world maps
polyconic/conical
equidistant along each standard parallel and central meridian
uses: topo maps; USGS 7.5 and 15 min quadrangles
4 Commonly Used Map Projections in GIS
Geographic or Plate Carree Projection
-Common native projection for exchanging data
– Albers Equal-Area Projection
-No area distortion, good for the United States
– Lambert Conformal Conic Projection
-No shape distortion, good for the United States. Used by some
states for SPCS
– Transverse Mercator
-Used for UTM coordinate system. Used by some states for SPCS
Projected coordinates are
simple x,y coordinates based
on some linear unit (e.g., meters)
Important Coordinate Systems for GIS:
Geographic Coordinate System • Latitude/Longitude – Cartesian Coordinate Systems • Universal Transverse Mercator (UTM) • State Plane Coordinate System (SPCS) • Other Projected Coordinates
Topology can be different for ___ feature classes in the ___ feature dataset.
different, same
Rule about feature classes in feature dataset
All features contained in must be in same projection and
coordinate system
5 Components to GIS data quality
Positional accuracy
– What is the position (X, Y) accuracy of features?
• Attribute accuracy
– Are the attribute values correct for features?
• Completeness
– Is the dataset complete? Does it cover the entire geographic
area of interest?
• Lineage = documentation about how a dataset was
derived, what steps were performed on the data
• Logical consistency = consistency of the data to other
datasets and the “real world”
Mean Center
Calculates the mean or average x and y coordinates (centroid)
for a set of features (points, lines, or polygons)
Weighted Mean Center
Features with higher attribute values will have a greater weight in the output weighted mean center
Central Feature
Identifies the most central feature from a set of points, lines, or
polygons
– Unlike the Mean Center, the Central Feature is at the coordinate
location for a feature that already exists
How is the standard distance calculated?
Steps: 1) Mean center is calculated first; 2) the average distance from the mean center is calculated for all points (standard distance/deviation); 3) Circle is drawn centered on the mean center using the standard distance/deviation as the radius
-more clustered = smaller circle and vice versa
Standard Deviation Ellipse
Like standard distance, measures concentration of features but also the directional trend
- standard deviation is calculated for the x and y coordinates separately, creating long and short axes (x standard distance and y standard distance)
If the null hypothesis is rejected, what happens?
There ARE statistically significant patterns.
Average Nearest Neighbor Analysis
-Use for points, does not consider attribute values
-calculated by determining if the point locations are closer
together than what we would expect for a random distribution
-gives a z-score statistic
-reject null if z is less than -1.96 OR more than +1.96
Average Nearest Neighbor Z statistic interpretation
less than -1.96 indicates clustering whereas more than 1.96 indicates dispersion in the dataset
Global Moran’s I for Spatial Autocorrelation
- Use for polygons, DOES consider attribute values.
- Measures spatial autocorrelation
- one Z-Score value calculated for distribution
Moran’s I interpretation
- the null hypothesis is rejected if lower than -1.96 OR higher than +1.96
- Z-score less than -1.96 indicates dispersion, while a Z-score greater than +1.96 indicates clustering in the dataset
Hot Spot Analysis
-Use for polygons, does consider attribute values
To be a statistically significant high hot spot, a feature has to be
surrounded by other features with high values. Vice versa for low
hot spots.
To be a statistically significant high hot spot, a feature has to be ______ by other features with ___ values. Vice versa for low
hot spots.
surrounded, high
What is the output of hot spot analysis?
new feature class layer, each feature in the layer has a
Z-Score value.
– a Z-Score value of greater than +1.96
(high clusters, red by default) or less than -1.96 (low clusters, blue by default)
9 Types of NLC
- Water – Developed – Barren – Forested Upland – Shrubland – Non-Natural Woody – Herbaceous Upland Natural/Semi-Natural Vegetation – Herbaceous Planted/Cultivated – Wetlands
What is a datum?
A mathematical model of the Earth, which serves as the base for calculating the geographical coordinates in the case of a horizontal datum and for calculating elevations in the case of a vertical datum.
What is a horizontal datum?
Lat/long of an initial point (origin), an ellipsoid, and the separation of the ellipsoid and the Earth at the origin.
Will digital data layers based on the same projection but different datums register correctly?
Nope
What is a projected coordinate system?
It is built on a map projection. It is often divided into different zones to maintain the accuracy of measurements
ex: UTM, SPCS, UPS
