Module 8 Flashcards
Network
▪ a network is a system of interconnected lines (edges) and intersections (junctions)
that represent possible routes from one location to another
Geocoding
▪ central to the use and analysis of networks is the need for places/features/points of interest to be accurately
positioned along the network, as well as a mechanism to
find each location – known as geocoding
▪ every entity of interest has a location and geocoding
translates that location (eg, latitude/longitude) into a
more conventional location system (street address)
MAF/TIGER files
▪ the US Bureau of the Census produces the most widely used geocoded geodatabases, known as MAF/TIGER files ▪ these attribute fields allow input addresses to be found (matched) in the reference database ▪ in Canada, high quality geocoded data must be purchased (Canada Post is a crown corporation)
Unmatched records in Geocoding
▪ unmatched (or tied) records can be handled either by relaxing the tolerances on the automated process, or by manually assigning an address to each unmatched record ▪ the ‘interactive rematch’ option in ArcGIS allows you to view each unmatched address and compare it to likely matches ▪ this process is often iterative and takes time, but the goal should be to reduce your unmatched addresses to 0
Undirected Network Analysis has steps(4)
1.Collect Source-Network Information
-Photogrammetric/LIDARgrammetric
Digitization
2.Build Topologically Correct Network
Dataset Elements
-edges (derived from lines-direction,1way or 2way), junctions (derived from intersections-4way stop, yeild) and turns(left, right, U)
- Specify Network Analysis
- identify optimum route
- find closest facility
- identify service area
- identify optimum delivery route
- location-allocation modeling - Solve the Network Analysis Problem and
- Present Results
- cartographic display
- route instructions (turn-by-turn)
▪ in shortest path analysis, you can
choose between straight-line or trueshape
distance
▪ straight-line distance – as the crow files – is easily computed and doesn’t necessarily need a topologically correct network ▪ true-shape distance follows the network of paths, producing a more realistic measure of distance
location-allocation modeling
: finding the best locations for one or more new
facilities that will service a given set of points and then assigning those points to
the facilities, taking into account factors such as the number of facilities
available, their cost, and the maximum impedance from a facility to a point
Location-Allocation types:6
- Target Market Share
- if money is available, helps facilities understand where they could grow in future - Maximize Market Share
- competing facilities will benefit from closer proximity - Minimize Impedence
- reduce travel time - Maximize Attendence
- how easy is it to travel to your location - Minimize Facilities
- same as maximize coverage but based on a restricted number of facilities - Maximize Capacitated Coverage
- capture people where demand exceeds supply - Maximize Coverage
- increase the ammount of people within the coverage area
Directed Network Analysis has steps(
- Collect Source-Network Information
- GPS
- Photogrammetric/LIDARgrammetric
- Digitization
2.Build Topologically Correct Network Dataset Elements edges (derived from lines) junctions (source and intersections) point and area ancillary features -all causing impedence
- Specify Network Analysis
- identify optimum route
- find closest facility
- identify service area
- identify optimum delivery route
- location-allocation modeling - Solve the Network Analysis Problem and
- Present Results
- cartographic display
- route instructions (turn-by-turn)
Directed vs. Undirected
▪ directed networks differ from undirected networks in
that travel is allowed in only one direction
Define Source Junctions and Sink Points
Directed Networks
▪ source junctions provide the material to the
network and pushes the material away from
itself (eg, the main sewer in your home)
▪ the sink point is the location where the material
or commodity is used, collected, or actually
leaves the network (eg, the sewage treatment
plant in the city)
T OR F
Only Undirected Networks have impedence
F bpoth do
Topology transforms the lines of the source network into …3
edges, junctions, and turns
Network cost=
impedence
barriers
.barriers are placeable objects in the network analysis and can be used to deny passage along an edge or through a junction
