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GIS 3426 MIDTERM Currit
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Gravity
Terms in this set (51)
Datum
a reference or base for all other measurements.
Families of Projections
Cylindrical, Conical, Azimuthal (planar)
Geographic Objects
Points, Lines, or area (polygons), or surfaces represented in GIS
Resolution
Types:Spatial, Spectral, temporal, and radiometric.
-the precision with which the phenomenon of interest can be described in Raster data sets.
-distance that one side of a grid cell
represents on the ground
Vector Data Sets
An object-based ontology describes the world as a space that is filled with discrete, identifiable units (i.e., objects) that have some sort of spatial reference, usually in the form of geographic coordinates
Raster Data Sets
location-based ontology that describes the world as a collection of spatial distributions of phenomena. In other words, for a particular attribute or theme we are interested in
Spatial Measurement Levels
Nominal, Ordinal, Interval/Ratio
Projection
A means of representing a spherical surface in a flat surface Projection
3 main Coordinate Systems
• Latitude/longitude
•UTM
• State Plane
Geographic Patterns
• Distance- Absolute/Relative
• Direction
• Arrangement
• Orientation
• Scale
topology
- Adjacency
- Connectivity
- Containment
Modifiable Area Unit Problem
a source of statistical bias that can radically affect the results of statistical hypothesis tests. It affects results when point-based measures of spatial phenomena (e.g., population density) are aggregated into districts. The resulting summary values (e.g., totals, rates, proportions) are influenced by the choice of district boundaries.
Dispersion
geographic process: Spread of attribute from one area to another
-Contagious Expansion Diffusion
-Hierarchical Expansion Diffusion
-Relocation Diffusion
How many zones are in UTM
There are 60 zones in the system, and each zone corresponds to a half cylinder wrapped along a particular line of longitude, each zone being 6 degrees wide.
How wide are the zones in UTM
Each zone is six degrees of longitude in width
Where do the zones in UTM begin
Zone 1 applies to longitudes from 180 W to 174 W, with the half cylinder wrapped along 177 W; Zone 10 applies to longitudes from 126 W to 120 W centered on 123 W, and so on.
Needs Analysis Examples
What are my questions? (What is the assignment?)
• What are the patterns I expect to measure?
• What are the causes and outcomes I plan to analyze?
• What data are available?
• Is the data of an appropriate detail to answer my questions?
Define Standards on Data format
OpenGIS Consortium
Defines Meta Data Standards
- FGDC Standards
Types of Scanning
- Flatbed
-Drum
-Line
Point Patterns
-The pattern is random (points are located independently, and all locations are equally likely).
-The pattern is clustered (some locations are more likely than others, and the presence of one point may attract others to its vicinity.
-The pattern is dispersed (the presence of one point may make others less likely in its vicinity).
Tessellation
exhaustive regular or irregular partitioning of
space
most commonly tessellation of squares
-also hexagons
- From remote sensing:
• Pixel (picture element)
• Raster (a row of a image)
Statistical Surface
- X, Y, Z Rasters
- Can represent natural or cultural phenomena
•elevation
• temperature, soil moisture....
• population, income....
Calculating slope for a curve at a point
( dy / dx )
Aspect
• Slope direction (aspect)
= angle of maximum slope
A = tan-1slope y / slope x
Visibility Analysis
>Use DEM to determine...
- From where can point X be seen on a
surface?
- What parts of the surface can be seen from
point X?
> Uses "line of sight" from observer point to
surface points to create intervisibility
matrix.
- Optionally uses observer height
First Law of Geography
• Everything is related to everything else,
but near things are more related than
distant things
Auto correlation
A statistical measure of how proximate
(i.e., ordered) objects are related
- Spatial
- Serial (i.e., time)
Surface Interpolation
• Creation of surfaces from point data
and
their attributes
- Global or Local Average
- Thiessen Polygons (Voroni diagrams)
- Linear Interpolation
• Trend surface analysis
- Weighted Distance
-krigging
Local Interpolation
use a neighborhood of sample points to estimate a
value at an unsampled location
Global Interpolation
use all known sample points to estimate a value at
an unsampled location
Inverse Distance Weighting
Regions of Influence: Criteria
- Distance
- Number
• Calculation
- Simple average: sum / total points
- Weighted average: sum of weighted points / total points
- Weight = 1 / distance from unknown point
POWER
Krigging
Uses distance AND probability
• Ordinary Kriging
- No trend
• Universal Kriging
- Trend without known model
parameters
• Simple Kriging
- Trend with known model
parameters
• Indicator Kriging
- Binary prediction surface
• Cokriging
- Multiple inputs
Theissen Polygons
to estimate rainfall at any point, take the rainfall measured at the closest gauge. This leads to a map in which rainfall is constant within polygons surrounding each gauge and changes sharply as polygon boundaries are crossed.
Centroid
is the most convenient way of summarizing the locations of a set of points.
Hillshading
Shadows drawn on a map to simulate the effect of the sun's rays over the varied terrain of the land
Nugget
can be interpreted as the variation among repeated measurements at the same point.
Sill
The value of difference of range.
Ansotropy
A property of a spatial process or data in which spatial dependence (auto correlation) changes with both the distance and the direction between two locations.
Voronoi Diagrams
are often used to delineate areas of influence around geographic features.
overlay
Boolean Operators: Intersection (and) Union (or)
Identity
Buffers
type of analysis function used for finding things within a specified proximity around a line, polygon, and or a point
Georeferencing
Defining a projection/coordinate system for
a raster
Primary Data
Collected by the User
•Raster
- Digital remotely sensed images
- Digital aerial photographs
• Vector
- GPS measurements
- Field survey measurements
Secondary Data
Collected By someone else
• Scanning
- Flatbed
-Drum
-Line
• Digitizing
- On-screen
- Tablet
Steps/How to to digitize (i think)
-Assign unique identifiers.
-Mark tic locations.
-registration and transformation
-Ensure the continuity of features across map sheet
boundaries
Iterative Processing
In hierarchical terms Data<Information<Knowledge.(Data leads to info which leads to knowledge.
Knowledge: The possession and understanding or relations between data.
Higher-level objects
Attributes determined from data
- (NOT stored in data)
• Points
- Centroids- Point patterns
• Lines
-Networks
• Polygons
- Landscape metrics
Scale vs Resolution
grid cell resolution
The higher the resolution
(smaller the grid cell), the
higher the precision, but the
greater the cost in data
storage
Difference in interpolation vs extrapolation
interpolation -- estimating values within a series e.g. 1.2.3.x.y.6.7 (x = 4, y = 5)
extrapolation -- estimating values outside a known series e.g. 2 4 6 x y (x = 8, y = 10)
Variogram
Findings of a Krigging, describes the...
- Lag
- Nugget
- Sill
- Anisotropy
- Output
->Prediction map
->Standard error
-> Quantile map
- >Probability map
;