GIS Quiz 8

area suitability (site selection)

-determine which areas are best suited to certain applications by taking into consideration many relevant factors -many different methods have been developed to evaluate site suitability

common measurement of shape

-S=P/3.54*sqrt(A) -P= perimeter -A= area -normalized; the compactness of a circle is 1 -the more contorted the area, the higher the shape measure

issues with length measurement

-abstracted polyline is never a perfect representation of the real world equivalent -always tend to cut corners -length of polyline tends to be shorter than the length of the object it represents -exception is when the object is truly straight -measurements in GIS usually based on 2D features -an undulating surface won't be accounted for -measurement may be substantially shorter than reality

heuristics

-algorithms designed to work quickly -come close to providing the best answer without guaranteeing the best solution will be found

optimization

-analysis of patterns to create improved designs -GIS applications focus on design are normative uses -implemented as spatial decision support system

descriptive summaries

-attempting to summarize useful properties of datasets in one or two statistics -borrow many concepts and techniques from non-spatial statistics

measurement of area

-based on coordinates of polygon vertices -breaks complex shapes into a series of trapezia -area of these is then calculated and summed -area outside of the polygon is subtracted from this sum

density estimation

-creates interpolated points from known samples -creates a field from discrete objects -field's value at any point is an estimate of the density of discrete objects at the point -should not be applied to continuous fields

major steps of boolean overlay analysis

-data processing: collect datasets that represent the individual requirements -suitability ranking: suitability of each dataset is determined using binary logic -overlay: intersection of suitable areas from each dataset will be the areas that satisfy all the pertinent requirements

indexing

-datasets evaluated may be quite diverse -overlaying these factors in their raw form will not produce a meaningful result -ordinal measurement scale is applied to each of the datasets

density dot mapping

-effective -objects remain discrete

spatial decision support system (SDSS)

-enables GIS to provide instant feedback upon what if scenarios -need geographic analysis to make a decision

routing problems

-ensures the path of a vehicle is the most efficient one possible -service vehicles, delivery trucks, etc. -constrained to a given network -discrete rather than continuous -based on the shortest path

measurement using GIS tools and digital databases is

-fast -reliable -accurate

the traveling salesman problem

-find the shortest tour from an origin through a set of destinations and back to the origin -potential number of tours will grow exponentially with each additional destination -GIS designed to employ Heuristics

weighted overlay

-if parameters are continuous in nature then the overlay of discrete objects will be insufficient -overlay of continuous data requires continuous datasets -spatial analyst permits the conversion of discrete data into continuous data -useful when attempting to compare both data types

fragmentation statistics

-measure the degree of fragmentation of spatial data sets -useful in landscape ecology -habitat fragmentation affects the success of a certain species -plant/animal pops less likely to survive in highly fragmented landscapes that have potentially dangerous regions between habitable patches

point of minimum aggregate travel (MAT)

-minimizes the sum of distances from each point to the center -may be a good candidate point to site any central service such as schools and hospitals -no simple mathematical expression

dispersed distribution

-negative spatial autocorrelation -presence of one point may make others less likely in its vicinity -commonly the result of competition for space

various indices of fragmentation

-number of patches -size distribution -average shape of patches

boolean overlay based analysis

-operation is via polygon overlay -also called sieve mapping process

centroid (mean center)

-point at which an imaginary, flat, weightless, and rigid map would balance perfectly if weights of identical value were placed on it so that each weight represented the location of a single entity within a population -found by taking the weighted average of coordinates

random distribution

-points located independently -all location are equally likely

clustered distribution

-positive spatial autocorrelation -some locations are more likely than others -presence of one point may attract others to its vicinity -identification is necessary first step prior to isolation of a cause

shape and gerrymandering

-process of redrawing political boundaries in a manner to provide a group or political party an advantage -cracking and packing -districts are created in GIS

measures of spatial pattern

-random -clustered -dispersed

measurement of shape

-shape is a property of many objects of interest in geography -description of which may be verbal

kernel function

-shape of the kernel is dependent upon a distance parameter -increasing the distance produces a broader, flatter shape -kernels summed to produce a composite surface -smoothness of the resulting field depends on the width of the kernel -kernels should merge together to produce a continuous surface

great circle metric

-shortest distance between two points on a spherical globe -decimal degrees -lat/long

pythagorean/straight-line metric

-simplest metric -shortest distance between two points -only suitable for planar projections

weighting

-some criteria are more important than others -order of importance may be implemented by weighting the indexed datasets

network distance

-sum distance of network segments along a travel route must be calculated -each segment is calculated using the pythagorean metric

choropleth mapping

-units may be contiguous, but still discrete -internal variation within mapping unit is removed by the areal averaging process

dispersion

-used to measure spread of points around a center -mean distance from the centroid is a simple measurement of dispersion in 2D

kernel density

-values associated with each point are spread out, starting from the point location, to the specified radius -density is greatest at the point location -diminishes to 0 when reaching the specified radius

packing

concentrating the opposing party's voting power into one district

cracking

minimizing the voting power of the opposing party's supporters by spreading the across districts

point density

points or lines that fall within the search area are summed then divided by the search area size to get each cell's density value

major drawback of boolean logic

produces abrupt discontinuities that don't reflect the continuous nature of many controlling factors

metric

rule for determining distance between points in space