Short answer. A lot of things, especially:
Connectivity and Impedance Values
My suggestion is to get more familiar with NA by working through the tutorial.
I am not familiar with the OSM data quality of the London area, but when I used OSM Data from Hamburg with the Network Analyst I for example had problems with oneway streets (editing needed for ArcGIS to recognize them properly), prohibited turns onto highways (missing z-levels, bad connectivity set-up) and maxspeed data (many values not existent).
Not being able to perfom some types of analysis like Closest Facility seems rather odd though. What exactly happens when you try to do that?
Location XY is on a non-traversable network element position.
Warning: 0 location(s) in "Incidents" are valid. Need at least 1 valid location(s).
Warning: 0 location(s) in "Facilities" are valid. Need at least 1 valid location(s).
Error: Insufficient number of valid locations in "Facilities" or "Incidents".
My minute Field rows are all null value, how can I calculate this to return figures?
Your Incidents and Facilities are on street elements that are either not connected to the rest of the network (for example because of little gaps from the endpoints to the next street elements), or there are some restrictions active that prevent using this street (use the network identify tool to check, or turn restrictions off in the analysis settings).
For example with the field calculator and a little math using a speed value (30mph?) and the shape length attribute.
Hi Olawumi Lanlehin,
Have you figured out the problem with London road network?
Currently, I am doing my dissertation and I need to run a network analysis (Closest facilities) on London roads. I have a similar problem as yours and was looking through websites and blogs to find a solution which I came across to the discussion that you've started.
I just was wondering whether you might be to help me now. Many thanks in advance.
looking forward to hearing from you.
If you are using Open Street Map data, I would suggest that you look at the tools at the link below to help build a network dataset that can be used with ArcGIS.
Alternatively you can use the closest facility service on ArcGIS.com and do your analysis there. You will be paying some credits to use that. But the network of London is available ready to use.