[R-sig-Geo] [FORGED] Create a Spatial Weight Matrix based on road distance

Juan Pablo Carranza c@rr@nz@ju@np @end|ng |rom gm@||@com
Sun Jun 23 07:17:18 CEST 2019


Hi all!
I don't have the specific answer, but I don't appreciate academic bullying
either. So... here is a way you could take. Go to qgis, calculate road
distances by network analysis and then add it to your dataframe. Use this
new variable to weigth the matrix.
I hope this serves, and I hope Rolf solves what ever is bothering *him*.
Cheers

Juan Pablo Carranza
Mgter. en Administración Pública
Lic. en Economía

El dom., 23 de jun. de 2019 1:16 a. m., Rolf Turner <r.turner using auckland.ac.nz>
escribió:

> On 23/06/19 3:30 PM, Rolando Valdez wrote:
> > Sorry again.
> >
> > A Spatial Weight Matrix (swm) is an object used in spatial econometrics
> > to characterize the spatial structure among territories. It is an
> > element nxn where n is the number of territorial units (counties,
> > districts, states, cities, regions) in the sample and it could be based
> > on contiguity or distance. Usually, you can create a swm based on
> > distance using 'dnearneigh' from spdep and then convert to a listw
> > through 'nb2listw'. The problem is that the matrix that you generate
> > trough 'dnearneigh'computes the euclidean distance among centroids of
> > polygons. This is where I spot my issue, I need to compute the swm using
> > the road distance instead of euclidean distance computed through
> > 'dnearneigh'. I do have a shapefile with poligons (counties) and another
> > shapefile with lines (roads).
>
> OK.  It's getting a *bit* clearer ....  You are interested in "road
> distances" between counties.  I'm still not entirely sure what this
> means.  Is it the *minimum* distance by road from one county to another?
> In which case, if two counties are contiguous (adjacent) and there is a
> road crossing the border between the two, is the distance between the
> counties equal to zero?  (This doesn't seem like it would be
> satisfactory ....)
>
> If this is not the case, then what *is* the case?  Perhaps you want
> distances between the *centroids* of the counties.  What then do you
> mean by road distance when the centroids do not lie on a road?
>
> You apparently need to deal with counties in which there are no roads at
> all.  To handle this you have to define what *you* mean by the distance
> by road from county A to county B when there are no roads at all in
> county B.  Perhaps infinity would be the appropriate distance, but *I*
> don't know; you have to make the call.
>
> Previously you indicated that you needed to know (pairwise) road
> distances between specified points in a given set, and I showed you how
> to obtain those using pairdist(), from spatstat.  Now it seems that you
> want something rather different, and it's still not clear what.
>
> You need to get *your* thoughts clear; make some definitions and
> specifications, and decide what you really want or need.
>
> It seems that you are expecting R to magically do your thinking for you;
> it won't!
>
> cheers,
>
> Rolf
>
> > El sáb., 22 de jun. de 2019 a la(s) 20:00, Rolf Turner
> > (r.turner using auckland.ac.nz <mailto:r.turner using auckland.ac.nz>) escribió:
> >
> >
> >     On 23/06/19 2:38 PM, Rolando Valdez wrote:
> >
> >      > I am sorry, I was not clear enough. My goal is to calculate a
> >     spatial
> >      > weight matrix (nxn) across counties but, instead of euclidean
> >     distance,
> >      > to use road distance.
> >
> >     I'm afraid I still don't understand.  To put it mildly. You
> presumably
> >     have a clear idea of what you are trying to, but those of us who are
> >     not
> >     involved in your research have no such idea.  We (or at least I)
> >     haven't
> >     a clue as to what you are talking about.
> >
> >     What do you mean by "spatial weight"?  What are these weights used
> for?
> >     What is n?  How are the counties involved?  Is n the number of
> >     counties?
> >     Are you interested in the road distance (minimum road distance?)
> >     between
> >     pairs of counties?
> >
> >     Please explain *clearly* and do not expect those who are trying to
> help
> >     you to be mind-readers!!!
> >
> >     cheers,
> >
> >     Rolf
> >
> >      >
> >      > El sáb., 22 de jun. de 2019 a la(s) 19:28, Rolf Turner
> >      > (r.turner using auckland.ac.nz <mailto:r.turner using auckland.ac.nz>
> >     <mailto:r.turner using auckland.ac.nz <mailto:r.turner using auckland.ac.nz>>)
> >     escribió:
> >      >
> >      >
> >      >     On 23/06/19 1:17 PM, Rolando Valdez wrote:
> >      >
> >      >      > Thank you for your answer.
> >      >      >
> >      >      > I have a shapefile with, say, counties, and I got another
> >      >     shapefile with
> >      >      > the roads. ¿What if a county does not intersect any road?
> >      >
> >      >     I am sorry, but it is not at all clear to me just what the
> >     problem is.
> >      >     How do the counties come into the picture?  You said you
> >     wanted to get
> >      >     the road distance between points on the roads.  What have the
> >     counties
> >      >     got to do with this?
> >      >
> >      >     Can you perhaps provide a reproducible example?
> >      >
> >      >     cheers,
> >      >
> >      >     Rolf
> >      >
> >      >      >
> >      >      > El jue., 20 de jun. de 2019 a la(s) 19:08, Rolf Turner
> >      >      > (r.turner using auckland.ac.nz <mailto:r.turner using auckland.ac.nz>
> >     <mailto:r.turner using auckland.ac.nz <mailto:r.turner using auckland.ac.nz>>
> >      >     <mailto:r.turner using auckland.ac.nz
> >     <mailto:r.turner using auckland.ac.nz> <mailto:r.turner using auckland.ac.nz
> >     <mailto:r.turner using auckland.ac.nz>>>)
> >      >     escribió:
> >      >      >
> >      >      >
> >      >      >     On 21/06/19 12:26 PM, Rolando Valdez wrote:
> >      >      >
> >      >      >      > Dear community,
> >      >      >      >
> >      >      >      > Is there any way to create a spatial weight matrix
> >     based
> >      >     on road
> >      >      >     distance?
> >      >      >      > I am trying to use the road distance between two
> points
> >      >     instead of
> >      >      >      > euclidean distance.
> >      >      >      >
> >      >      >      > I've seen that there is a package named osrm. Can
> >     anyone give
> >      >      >     some advice?
> >      >      >
> >      >      >     I don't know anything about "osrm".  Calculating "road
> >     distances"
> >      >      >     can be
> >      >      >     done in the spatstat package reasonably easily, if you
> >     take
> >      >     the trouble
> >      >      >     to represent your collection of roads as a "linnet"
> >     object.
> >      >      >
> >      >      >     Given that you have done so, suppose that your linnet
> >     object
> >      >     is "L" and
> >      >      >     that you have vectors "x" and "y" specifying the
> >     points on L
> >      >     (i.e. on
> >      >      >     your roads) between which you want to know the
> distances.
> >      >      >
> >      >      >     Do:
> >      >      >
> >      >      >           X    <- lpp(data.frame(x=x,y=y),L)
> >      >      >           dMat <- pairdist(X)
> >      >      >
> >      >      >     The object "dMat" is a (symmetric) square matrix;
> >     dMat[i,j]
> >      >     is the
> >      >      >     distance between point i and point j.  (Of course the
> >      >     diagonal entries
> >      >      >     are all 0.)
> >      >      >
> >      >      >     If your collection of roads is specified by means of a
> >     shapefile,
> >      >      >     vignette("shapefiles") will tell you how to turn this
> >      >     collection into a
> >      >      >     "psp" ("planar segment pattern") object; the function
> >     (method)
> >      >      >     as.linnet.psp() can then be used to turn the "psp"
> >     object into a
> >      >      >     "linnet" object.
> >      >      >
> >      >      >     HTH
>
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