Hot answers tagged network
20
GRASS v.net.iso will give you a result like this in this example.
You might not want to run a convex hull algorithm on this output. Imagine the blue roads: A convex hull around them would contain a lot of parts that are not reachable in the time represented by "blue".
Instead, you might want to look into alpha-shapes (related question: Concave Hull: ...
14
The geometric network is used to model things like utility networks, drainage, or any other network where the commodity does not have free will.
Network dataset is used for networks where "an agent" can choose the path, such as transportation networks.
There a description here (scroll down to the What is a network? section):
...
11
[Edit: this has been superseded by nx_spatial which is available from pypi (easy_install nx_spatial). Importing shapefiles is now standard in networkx 1.4]
I've been kind of disappointed by the lack of geometric network tools in ESRI's Python GP API, so I wrote up something that loads Shapefiles and Feature Classes into networkx directional graphs ...
10
If you are mostly interested in traversal/routing, go with pgRouting.
If you don't find what you need to do there, networkx has a freakishly large number of algorithms for graphs and now loads shapefiles out-of-the-box using OGR.
nx_spatial extends networkx in some minor ways mostly related to utility networks.
9
There are different methods depending on what you want to accomplish, how much data you have, and how pretty you want it. Your idea is a good idea and would probably work well. Of course another obvious answer is to show all of the relationships all the time but that would add a lot of visual clutter. Perhaps a nice compromise is to always show all of the ...
8
Have you thought about using an IaaS such as Amazon Web Services to host your GIS stack? There are a bunch of Amazon Machine Images (AMI) that already fulfill your requirements. You could spin up an Amazon EC2 instance to run your GIS jobs and manage it remotely from your laptop.
Here is a course that could get you spun up fairly quick (look at lessons ...
7
If you have the roads in a spatial form, such as a Shapefile, you can load them into PostGIS and have it automatically find those using an SQL query. I've done this before - the SQL statement is designed to find for each road those that intersect geographically and create a nodal point for each crossing.
I will try to clean this up later, but here is the ...
7
There is an interesting project from Ilya Boyandin on the go - JFlowMap.
It's not yet publicly available but screenshots look very promising indeed. More info here and here.
You might be also interested in browsing some of the papers about movement geovisualization from Natalia & Gennady Andrienko.
UPDATE: GraphRECAP and FlowMap might also be of ...
6
Well, potentially you could use v.net.iso from GRASS GIS. However it doesn't create polygons (AFAIK), but splits the lines by cost classes from the source.
As for calculating drive times from OSM, you could import the data into GRASS with v.in.osm, and use the v.net.iso to calculate the cost zones. If you wanted travel times and you don't have road speed ...
6
Jay has covered a lot of the suggestions that I immediately thought of from the visualisation angle. However, does it have to be a network? Depending on the needs of the user and the clustering of the data a better solution may be to show relationships with color coding rather than lines.
My suggestion: when a user clicks on a point then all the related ...
6
Two tools I could suggest for some exploration:
NetworkX python library;
Gephi platform, especially with GeoLayout plug in.
In both solutions you could specify geographic coordinates as the position of nodes and the get nice flow representations by intensity and/or direction.
None of these tools offer easy export to web map, but with little bit of ...
6
My basic intuition would be displaying the data as a graph, not as a map. Think of it as a subway line map: It does not display the lines on a geographic map, but as abstract lines which intersect on junctions. That way you can focus on the important part (i.e, the next station; how to move from one line to another) instead of being distracted the actual ...
6
You can analyze polylines in amazing ways by using buffers. This is usually inefficient--buffers create many additional vertices--but (a) it is a technique available in many GISes (vector or raster based) and (b) it sometimes can produce information that is otherwise hard to get.
In this case, buffering the road by a small amount and then buffering by the ...
5
You might want to browse this post:
Alternatives to pgRouting
and look through the previous posts using the Network and Routing tags
5
Check out the OpenGraphRouter project.
Stephen Woodbridge has created a demo demonstrating the driving directions.
There is a pretty good thread on the PostGIS-users list related to this.
5
What licence level is your ArcMap?
Intersect should work with a set tolerance.
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//00080000000p000000.htm should create a new polyline with nodes where your vertices were.
You will need to rebuild your network afterwards
5
Firstly, I am not clear on what kind of output you expect. Do the red and blue vertices consist of pairs? (i.e. do you want the shortest path from one of the red vertex to a specific blue Vertex?)
You should have a look at creating shortest routes
This requires all the stops that you route must past through. So assuming that your requirement is the shortest ...
5
I'm not sure exactly what your canal shapefile looks like, but here's how I would do that without using Network Analyst:
In the likely case that your Canals.shp polylines are split into separate but connected segments, use Dissolve to unsplit them. Then run Select by Location, finding features in Canals.shp that INTERSECT or BOUNDARY_TOUCHES with ...
5
I did! =)
Watershed command are working right now. I regenerate outlet points and I could get the correct pour points.
In other hand, I followed another method. Instead using Zonal Statistics, I did iteratively for each outlet point as follows:
Generate watershed [watershed];
Select withdrawals within the watershed [select by location];
If the count of ...
5
I've described how to calculate service areas aka catchment zones in Catchment Areas with pgRouting driving_distance()
and related posts. All of them use QGIS and pgRouting - a routing extension for PostGIS databases.
5
NetworkX ( A python module for the creation, manipulation, and study of the structure, dynamics, and functions of complex networks ) has a read_shp() function which generates a graphs from shapefiles. You might want to check it out. Here's a short tutorial.
No TPSLIB export as far as I know but does support writing the graphs into formats like GML, GraphML, ...
5
I had to do this just recently. Using ArcGIS 10:
If you only want to symbolise the dead ends you can just set up a Topology on the roads featureclass and set the rule "Must not have dangles". this will put a marker on every feature that has a dead end.
Alternatively, run the "Feature Vertices to Points" Tool (Located in Data Management Tools --> Features) ...
5
If your facilities and incidents are both feature layers, and you only care about finding the closest (and not 2nd closest, 3rd closest, etc.) then you can just run Spatial Join. Set your incidents as the target_features, facilities as join_features, and closest as the match_option, and it will join the attributes of the nearest facility to each incident.
4
There's Flowmap, a niche GIS package designed for dealing with network analysis issues.
If you have a fairly simple use-case, the QGIS-based Quantum Navigator might do the trick.
GRASS also supports network analysis, though it may not be worth the friction of getting things set up inside of the environment.
4
This is a hard problem that as far as I know is not solved. A look at the current literature (http://scholar.google.com/scholar?hl=en&q=spatial+interaction+data+visualization) seems to support this view. Alisdar Rae has some interesting maps in ...
4
Your could use pgRouting with Quantum GIS.
This page from underdark's website explains how to do.
Good luck !
4
I would approach this as two separate problems. First, the individual line segments must be dissolved into connected components; just dissolving all of them on a default value won't work. This is a graph theory problem, and what we want are the "connected component sub graphs".
I'm sure there's a way to hack this with network analyst, but my preference ...
4
As with everythin in GIS there's more than one way to do it:
ArcGIS has a feature to do just this, See Divide line function. Of course, remember that you rarely have an exact division unless you use the percentage option (i.e. you will get a bit left over). And, to be honest, I found it would not always work perfectly but it doesn't do too bad a job. ...
4
I beleive your problem, as @whuber, suggested would best be represented in an Adjacency Matrix. That is, if you have the time and inclination to understand the theory behind it, rather than relying on a package to do the job for you.
For a given graph G, with vertices of {v1, v2,...,vn} where n is the number of vertices, you need to create a matrix of size ...
4
A Solution can be found via:
"Using GIS for Decision Support in Emergency Medical Services" Example
Programs required:
QGIS (with GRASS)
OpenOffice
R
"To conduct an analysis of ambulance service areas, Geographic Resources Analysis Support System (GRASS) was used within Quantum GIS (QGIS). GRASS is included with the QGIS download. One of the benefits ...
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