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79 Cards in this Set

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Types of vector data analysis
buffering, overlay, distance measurement, network analysis
Most common analysis of spatial data is what:
buffer and overlay
buffereing is:
creating a proximity area around a selected point line, or polygon
what is a buffer zone
the newly created area within a specified distance from the selected features
A buffere is a:
polygon created at a specified distance from a point line or polygon
a buffer around a point is:
circular zones
a buffer around a line is
elongated polygons following the line feature, the polygong doenst' have to be on both sides of the line
a buffer around a polygon is
a zone extending outward from the polygon boundaries
Buffer issues:
1- you never want to forget the untits youw ant to use,
2- dissolving vs. not dissolving
3- use of different buffer distances
4-variation of buffere distances
5-multiple buffer zones
6-inclusions zones vx. exclusion zones
What is dissolving:
removing intersects of buffer zones so it is one seamless polygon feature
what is overlay:
MOST POWERFUL feature of modern GIS.
It is the ablitly to place the cartographic representation of a thematic information of a selected theme over that of another
what is site suitablitly?
examines social, economic, physical, biological and other criteria to locate potential sited for some purpose (part of overlay)
what do overlay opperations combine:
geometry and attributes of two feature maps to create an output
Overlay procedure requires:
an input map layre and an overlay map layer
what can an output layer be in overlay:
point, line, or polygon layer
what must the overlay map layer and input map layer have in common:
the same coordinate system
The input layer can be what:
a point, line or polygon
The overlay layer must be a what:
a polygon ***
type of overlay polygong operations:
1- point-in-polygon
2- line-in-polygon
3- polygon-in-polygon
What are the common overlay methods:
union, intersect, and identity
Union overlay method is what:
-both input/overlay =polygon layers
-combines the area extent from both maps
Intersect overlay method is what:
-preserves only features that are within common area
-output feature have attribute data from both layers
-input layer can be a layer of point, line or polygon
Identity overlay method is what:
= OR and AND [(Input layer) AND (overlay layer)] OR (input layer)
-preserves features that are within common area and features from input layer
-input layer can be a layer of point, line or polygon
Buffers can be combined with what to analyze spaitail information:
polygon overlayes
What is vector line length:
length of straight line calculated by pythagorean theorem using beginning and ending point locations

-length of curvillinear line calcultaed by adding lenghts of individual line segments

-uses coordinate system to figure out measurements
To calculate area of vector polygon you:
break complex polygon into simpler geometric shapes such as right triangles and rectangels whose area can be calculated
Map manipulation is what:
no attribute data combination, just about the geometry
Examples of map manipulation are what:
dissolve, clip, merge
Map minipulation clipping is:
cutting out a section of city (cookie cutting) ex. you could get jsut the roads of the city
Map minipulation merging is what:
seamless layer, erase
Raster data analysis is based on what:
based on cells and grids
Raster data analysis can be performed on what:
-individual cells
-a group of celss
-an entire grid
-a set of grids
Common Raster data anaylsis operations:
-local operations
-neighborhood operations
-zonal operations
-distance measurements
What do you have to do before starting a raster data analysis:
set up the environment covered by the analysis
TO set up the env. covered by the analysis you can:
-difine the extent of the environment (area extent-ArcView) (set window- ArcInfo)
-Define the size of the output grid cells (the size of the input grid cells) (set cell (ArcInfo))
What is a mask grid in raster data anaylsis:
-a grid (or set of grids) used as a way to difine the area extent of the analysis
-in that case the extent of the analysis is defined by the cells of the mask grid that do not have a value of "no data" ("no data" is different from the '0' value)
Raster data anaylsis common operation: LOCAL OPERATION
-core raster data anaylsis
-consists of cell-by-cell operations based on preset or made up functions
Local operation: types of functions include:
*applied by one cell at a time
*can be applied on single grid or with multiple grids
Local operations with a single grid:
each cell value in the output grid is the result of the mathematical operation using the corresponding (overlapping) cell value in the input grid
ex. -floating point grid to integer grid -slope in percent to slope in degrees -universal soil loss equation
Local operations with several grids;
-similar to vector overlay anaylsis
-allows more possiblities for local operations ex. the combine operation (several grids)
Raster data anaylsis common operation: NEIGHBORHOOD OPERATIONS
-involves a focus cell and a set of cells in its vicinity (neighborhood)
-the value of the focus cell is computed with the values of the selected neighbor (surrounding) cells
-the selection of surrounding cells is based on the distance &/or the directional relationships to the focus cells
-the operation may or may not use the focus cell value
Some neighborhood operations:
-* x-by-x window = (ex. 3x3) the focus cell is always in the middle (most commonly used)
-circle neighborhood= figure out radius of circle & figures out the cell values inside circle
-Annulus = (doughnut shaped) cells that fall into the doughnut are used for computaion
-wedge neighborhood= cells insde the wedge are used. ex. data simplification and terrain analysis
Raster data anaylsis common operation: ZONAL OPERATIONS
*operation used to describe the geometry of zones (in a single grid) or to summarize the cells values by zone.
zones, disconnected zone, continuous zone
a zone is:
connected (continous zone/1 region) or disconnected groups (2 regions)of cells with same values
Characterisitcs of zonal operations:
zonal operations are performed either on a -single grid (discription of zone geometry) or on two grids (summary of cell values by zones)
Description of zone geometry (on single grid)
area is the sum of cells times cell area
ex. cell size = 2m => Cell area = 4msquared
Zonal operations perimeter:
it is the sum of the lengths of the boundary of each region of the zone
ex. cell size =2m
Zone B : perimeter = 2x10=20m (you get 10 by counting the sides of the cells you want to caluculate)
Zonal operations thichness:
radius (in cell length) of the largest circle that can be drawn within each zone
Zonal operations centroid:
consists of the parameters of the ellipse that best approximate each zone: centroid, major axis, minor axis
(major axis is the longest one, centroid is point in middle, minor axis is the smallest)
Using operation syntax to summarize cell values by zones (on two grids) you:
used input, zonal operator, and zonal grid to get an output grid
Raster data analysis common operation: DISTANCE MEASURE OPERATIONS
-extended neighborhood operation or global operation
-it consists of calculated distances away from source cells in a single grid
Princle of distance computation:
it is based on the node-link relationship
*node is VERY import. for computation - there are diagonal link, and lateral link , reference cell and direct neighbor cells
Princle of distance compuation:
-its node represents its center
-its links are the segments connecting its node to the nodes of the adjacent celss
-direct neighbor is a cell connected on the side (lateral link)
-diagonal neighbor is a cell connected by its angle (diagonal link)
Line Length (raster)
from node to node (not side to side)
Physical distance measure of application of distance measurment operations:
-straight-line distances away from source cells (similar to a buffer or source cells with continuous distance ex. buffer around stream network)
-reclassification=> discrete/homogeneous zone
-slice operation => equal-area/equal-interval zones)
-Allocation (allocaion grid, watershed)
Raster Anaylsis tools: overlays
called Map Algebra (you can +, - , / ) can make use of more than 2 layers
another name for terrain:
land surface
Land surfaces are:
-undulated, continuous, and 3D
-they are measured and anylays generaged from elevation data
elevation data of land surfaces include:
-slope(rate of change in elevation0
-apect (orientation of slope)
-stream network
-flow accumulation
The Z value in terrains:
-represent the elevation data in GIS
-they are not stored as part of the coordinate system, but as attribute data (vector data z value sotred in numerical field of attribute tabel, in raster data z is stored as cell values in grid)
Common data for terrain analysis
DEM- most common input data for terrain anayl.
-its quality determines the accuracy of the anaylsis
-needs to be converted to specific software format (grid for ArcView/ArcGIS/ArcInfo)
Terrain Maping includes:
contouring, vertical profiling, hill shading, hypsometric tinting, and 3D View
Terrain Maping CONTOURING:
ISOLINE-line connecting points of equal value in a thematic map
CONTOUR LINE: line connecting points of euql elevation-it is the isoline for a topographic map
CONTOUR INTERVAL- verticle distance between two consecutive contour lines
Goal of contouring:
gerated contour line or isoline to show the distribution of continous phenomenon
Caseof elevation in contouring:
-close contour line=>steep terrain
-'V' indicate stream direction (pointing upstream)
-traditionally helps calculate slope
construction of diagram showing the change in elevation along a line on a map
Goal of Vertical Profiling:
vizualize the changes in elevation along a linear feature of the map, or along a user difined line
Terain Mapping: HILL SHADING:
it is the simulation of the image of a terrain under the sun light
-slope facing incoming light are bright while slopes opposite to the sun are dark
Goal of Hill shading:
display the shape of lang features
Hill shading is also called:
shaded relief and shading
consists of displaying the elevation zones in different colors
Goal of hypsometric tinting:
to visualize the progression in elevation
Another name for hypsometric tinting
layer tinting
Terain mapping:PERSPECTIVE VIEW (3D)
it is the thre dimensional view of the terrain
Perspective View is controlled by 4 parameters:
1) The viewing azimuth- angle between north and the line defined by the target (on the surface) and the point of observation=> 0`-360`
2)the viewing angle- angle between the surface (horizontal) and the line defined by the target (on the surface) and the point of observation=> 0`-90` (@90` no longer view it as 3D but as 2D)
3) the view distance- distance b/w the ovbservation point and the target
4) the z-scale or verticle exaggeration factor- ratio b/w the verticle and horizonal scales
Terrain Mappaing: 3D DRAPING-
superimposition of thematic layers with a perspective view
Terrain anaylsis- SLOPE:
it is the rate of change in elevation
-percent slope= (verticle distance/horizontal distance)x100
-degree slope= arctan (verticle distance/horiz. distance)
Terrain anaylsis- ASPECT:
it is the orientation of slope (you can use 0`- 360` or cardinal orientation
Terrain anaylsis- VIEWSHED ANALYSIS:
*consists of using elevation grids to generate topography related hydrology features such as: watershed and sub-watershed, stream network, flwo accumulation (depth)
-DEM=> field elevation=> flow direction grid=> flwo accumulation grid