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Coalescing undermines the integrity of the network #126
In posts such as this one (http://kuanbutts.com/2018/04/01/spectral-cluster-transit/) and elsewhere, I have suggested that coalescing networks can improve speed.
This is true, but accuracy is sacrificed on graphs like a transit network.
In cases, such as a walk network, such a naive coalesce operation might be acceptable.
In the case of a transit network, we might effectively prune out critical edges such as those for providing transfers between routes (e.g. creating "free," immediate transfers from one line to another), thus artificially increasing accessibility.
This needs to be called out at least in a comment in the method. Better would be a way of improving the method to account for the transfer costs and keep different routes segmented.
referenced this issue
Feb 5, 2019
Profiled this operation's impacts on one accessibility measure (number of jobs each parcel get reach within a cost bound):
Seemingly it does not create a lot overly low accessibility measures but that needs further testing because that is a function of cost bound. For example, using max weight length has less impacts when we look at access to jobs within 60 mins than access to jobs within 20 mins.