Network Analyst: Network Dataset Creation Issues

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07-15-2010 03:24 AM
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New Contributor
Hi there,

I'm quite new to the network analyst toolset and would like to perform a basic service area analysis but I am having bit of trouble with creating a network dataset in ArcCatalogue...

I have ensured that the network analyst extension has been activated in Main menu\Tools\Extensions but when I right click on my source polyline shapefile (roads) in ArcCatalogue the "New Network Dataset" option is unselectable.

I have searched for a solution in the ArcGIS Desktop help function, the Network Analyst Tutorial .pdf document and various forums and I have reached the conclusion that that my input shapefile does not have the required fields in its attribute table and/or has polyline connectivity errors that prevent it from being used as source data for the creation of a network dataset.

So how do I make it work? I basically just want to calculate pedestrian travel times from certain points along (but unconnected to) a road network...

Any input and suggestions will be greatly appreciated!
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New Contributor III
Here is a quick checklist to help troubleshoot this issue:

  1. When you made sure the extension was checked on, did you do this from ArcMap or ArcCatalog? If you are trying to build the dataset in ArcCatalog, you must ensure the extension is enabled there. Ideally, if you are using Network Analyst, you should enable the extension in both ArcMap and ArcCatalog.

  2. Is your source polyline feature class really a shapefile, or is it perhaps a source feature class in a geodatabase? If it is a shapefile, then you should be able to right click on it to create a new network dataset, as you suggested. However, if it is a feature class in a geodatabase, then you must right click on the feature dataset that contains the source feature class to create a new network dataset.


If neither of these possibilities helps to resolve this issue, can you please post some screenshots showing that you have enabled the extension in ArcCatalog and that the "New Network Dataset" option is still disabled?
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Thank you for your assistance Michael, I was not aware that the extension had to be enabled in ArcCatalog as well... 😮

However, I am still encountering difficulties with creating a network dataset that allows me to calculate pedestrian travel times from certain points along (but unconnected to) a road network... In other words: I would like to generate consecutive travel time polygons (in minutes) originating from the amenities (points) along the road network/

Here is a edited screen shot of the polyline.shp and point.shp I intend to use for the abovementioned purpose:

[ATTACH]1774[/ATTACH]

Furthermore, I am unsure if the input roads shapefile must contain certain fields in its attribute table (it currently contains line segment lengths only) and if it must have a certain state of connectivity prior to creating a network dataset for the intended analysis to work. Will it be necessary to add any other fields to the attribute table or edit the current state of connectivity of the line segments?

Also, could anybody provide me with guidelines of what to do in the "new network dataset" wizard to prepare my network dataset to perform my desired analysis?

Any input and suggestions will be much appreciated!
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New Contributor III
Hi,

I am glad to hear that you got past your original problem.

As for your second problem of calculating travel time polygons for pedestrian travel times, your attachment appears to be invalid (i.e., I get an error message when I click on it). Please re-try attaching the image(s), and we can discuss this further.

Regarding your last question about what fields must be present for your network dataset, there are several levels of detail you can establish in your data, depending upon your modeling requirements. The most basic requirements would be for you to have some source of travel costs for your edges. This is often represented as either travel distance (e.g., using a length field) or travel time (e.g., derived from length and speed limit fields) or perhaps even both (modeled as separate cost attributes in your network dataset). A cost attribute is required to perform any realistic shortest path analysis on your network.

A next step would be to determine whether or not your data supports any restrictions for modeling real-world travel constraints on your road network (e.g., oneway streets or restricted turns). These can be modeled as restriction attributes in your network dataset. Oneway restrictions are often derived from simple boolean fields in your dataset (to indicate whether or not a street is oneway for a given travel direction). Restricted turns (or even turn delays) can either be modeled globally (i.e., applied universally to all possible two-part turns) or established for only an explicit set of turns in your network (this latter possibility requires you to create a turn source feature class).

Finally, you might also wish to establish support for generating driving directions on your dataset. This requires a street name field, as well as a specification of a length cost attribute and time cost attribute.

Of course, there are several other possibilities you might wish to consider when building your network datasets, but these are the most common. For a more detailed discussion of all of this (and more), including walkthroughs of building network datasets on sample data, I would strongly encourage you to work through the Network Analyst tutorial (this comes with your installation of ArcGIS). This includes examples of everything I have touched on above, as well as some more complex modeling scenarios. This is the best place to get started, and this will help you get a feel for how to setup your own network datasets using your own data.

If you have any further questions, please let me know.
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Hello again Michael,

despite your continued assistance I have not been able to conduct my desired analysis. I have tried to make it work until I figuratively got 'blue-in-the-face', but to no avail. Primarily I am struggling to create a new network dataset that is suited to my input data and analysis criteria.

I'm wondering if it is at all possible for you, based on the characteristics of my input data and desired type of analysis, to guide me step-by-step through the "New Network Dataset" creation wizard to achieve my desired results? I normally would not request something of this nature, but I am fresh out of university and a novice with network analyst and I am having trouble in specifying the right criteria in the "New Network Dataset" creation wizard to achieve the desired analysis due to my inexperience (I'm having trouble with determining the correct cost attributes for my network dataset/analysis in particular!).

I feel kind of silly to request this but I've virtually exhausted all other alternatives (including the network analyst tutorial) and my boss is sort-of on my back to get this done ASAP...

Here are my input shapefiles if you are interested in assisting me with this matter:

[ATTACH]1868[/ATTACH]

With this input data I would like to generate consecutive travel time polygons (in minutes) originating from the amenities (points) along the road network with the "Calculate Service Area" tool... It is therefore a very basic analysis with no restrictions for modeling real-world travel constraints (turns, driving directions, frictional surfaces, etc.). I keep saying to myself this can't be that difficult but I have had little progress and even less success... 

I will be very greatful if you were to put in some effort in my aid...
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New Contributor III
I would be happy to help you out and look at your data, but your attachments appear to be invalid (or unknown) file types. You will have to give me more information on accessing your files or upload a more appropriate file type (e.g., a .zip file with your data). If you are having trouble uploading files, please contact the site administrator for help.
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Sorry, I was under the impression that .7z files were okay to upload...:o

Here are my shapefiles in .zip format:

[ATTACH]1881[/ATTACH]

Thanks for your willingness to help Michael...
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New Contributor III
Zip files are certainly better, but the one you have uploaded is corrupted or invalid (try opening it to verify). There were problems at one point with attaching zip files to the forum postings; they were being corrupted. Perhaps this problem still exists. Please talk to the site administrators about this. I will see what I can do on my end as well.

In the meantime, please let me know specifically what is confusing you about creating your network cost attribute, and I will try my best to clear this up.
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