GIS second year exam Flashcards
Attribute selection selects a subset of features by preforming a select operation using…
Structured Query Language (SQL)
In vector analysis attributes can be created…
using existing functionality and adding item values to empty attributes
Spatial selections selects features on the basis of spatial relationships to other features and requires … input features
two
Buffering
The process of creating areas of calculated distance from a point, polyline or polygon
Polygon buffers can be…
outside, inside the line segment or both
A doughnut polygon buffer…
has a predefined range
Buffers can express suitability gradients but cause confusion when…
overlapping boundaries have not been resolved
Overlay operations allow the process of…
comparing features between multiple feature classes to allow spatial relationships between geographical coincident but different geographical phenomena to be studied
Set theory uses Boolean operations to allow overlays such as…
union, intersection and erase
Overlays can cause sliver polygons due to differences in data. They can be resolved by…
generalisation
Raster distance can be measured in a different ways such as…
Euclidean, Manhattan, proximity, proximity maps (buffering) and cost surfaces
How can proximity maps create buffers?
The proximity map measures distance as concentric equidistant zones and shows shortest straight line distance from cell to feature. Use the required buffer distance from feature and reclassify the proximity map
Reclassification…
replaces a cell of a particular value with a new one to simplify the raster data
Raster can also be overlayed - true or false?
True
In a local function…
the output value of each cell is a function of the corresponding input at each location. Value not location dependent
Local functions include…
exponential, reclassification and logarithmic
The output value of each cell is a function of the value of the input cells is a specified neighbourhood (e.g. 3x3) in a…
focal function
Focal and zonal functions include…
mean, stdev and sum etc
The output value at each location depends on the values of all input cells in an input value grid that shares the same input zone in a…
zonal function
In a global function…
output value of each location is potentially a function of all cells in the input grid
Global functions used for…
distance functions, surfaces and interpolation
An example of raster overlap mapematics is…
rainfall-evaporation=potential runoff
Spatial interpolation
Making an estimate of the value of an unsampled location using measurements made at locations in the same area
Spatial interpolation can be…
global/local, linear/non-linear and exact/inexact
The three methods of interpolation are
inverse distance weighted, triangular irregular network and global trend surfaces
Inverse distance weighted interpolation is calculated by…
using known values and weights based on distance (know the equation)
TINs calculate things like elevation by…
breaking area into a series of triangles and calculating each point based on the vertices
Global trend surfaces model unknowns using smooth mathematical functions (equivalent to polynomial regression) to produce interpolated general trends. It can be…
1st, 2nd or 3rd order and can derive trend for existing surfaces or for points
Interpolation approach for broad geographical trends?
Trend surfaces when being aware of generalisation
Interpolation method for complex spatial variation?
Inverse distance weighted or TIN
What are four things to consider in interpolation?
Representation, no. and location of points, boundary problems and parametrisation
In surface analysis, slope mapping calculates…
the maximum rate of change from each grid cell
What are the two components of slope?
Gradient and direction
What secondary features can be derived from a DEM surface?
profile curvature and plan curvature
Local Drainage Direction (LDD) Network is calculated to derive surface topology. What is this process?
Calculate steepest downhill slope within a 3*3 window and assign direction vector. This creates a raster where each cell contains the direction to the next cell
DEMSs can contain localised depressions called sinks (natural or DEM errors) that are removed when modelling hydrology. What are these?
They contain no output flow direction
How is flow accumulation calculated (also used to derive streams)?
By calculating the accumulated upstream cells of each cell which is based on flow direction grid (LDD)
How are watersheds calculated?
By calculating the upstream area that contributes flow to location from LDD network
What are two drawbacks of traditional Boolean land suitability approaches?
It’s too binary as assumes land always suitable and you cannot show which criteria are most important
MCE is the process of…
using multiple weighted criteria to quantitively evaluate the suitability of locations for a particular activity
What are the steps in a MCE?
Criterion preparation, standardisation, weights and constraints
Why do some data sets have to be prepared?
in MCE
Attributes like proximity to features have to be derived
What are constraints in MCE?
Boolean data-sets that represent areas that regardless of all other criteria considered are unsuitable for the problem being addressed
Why is criteria standardisation completed?
The unsure all criteria are expressed on the same measurement and scale
It is important that weights sum to 1 in MCE, what are two weight methods?
DIY and pairwise comparison
In a network model, what represents locations and connections?
Nodes and edges (or links)
What defines the connectivity of the network?/
Topology
Three uses of network analysis
fault-finding in utilities, hydrological modelling, transport route planning
Examples of weights in a network model
demand for nodes and travel time for edges
Directed networks are used for unidirectional things like waste water pipes and these models have some weights as bidirectional and some unidirectional. How to create a directed network?
Use the Utility Analysis tool to assign sinks and sources. Then set the flow direction to determine direction of edges in network so analysis can be performed
Additional network features
Centres (supply/demand maximum), stopes (transfer and costs), barriers (no movement) and turns (restrict direction)
The four network types.
undirectional/unweighted, undirectional/weighted, directional/unweighted,directional/weighted
The three network path analysis types.
shortest path analysis, origin destination analysis and location allocation analysis
shortest path analysis uses Dijkstra’s algorithm to…
find the shortest cost of moving across the network
Shortest path analysis can’t do travelling salesman problem but can do…
route by minimising topological edges, route by attribute weight and tour by attribute weight
Origin destination matrix uses origins and destinations to derive shortest path between all possible pair-wise combinations. It’s common to…
generate origins and destinations as centroids and then create link to real network during analysis
Location allocation analysis…
assigns locations via an analysis of their connectivity. Can be used for vehicle routing or classic allocation. Can be seeing how much of a network can access service or find closest service station
First part of Dijkstra’s algorithm.
Assigns initial distance of 0 for distance from origin to origin. Set distance to all other nodes as infinity. Set origin node as current node and other unvisted.
