[GIS] QGIS Distance Matrix Output

distance matrixqgis

I have a shapefile of points and want to measure the distance between each of them. After running the Distance Matrix command I get a matrix with distances as expected, but have no idea how to match each row (i.e. each point) to each other.

The problem arises because the names of the columns is not informative of which point each distance refers to.

Clearly the first column refers to the distance between each point and itself. But, for example, how do I know what two points define the distance in row 1, column 2?

Best Answer

Depending on what exactly you want to do with the data once you know the start, end and distance between the points you may find that the "Linear (N*k x 3) distance matrix" output matrix type is sufficient. This option is set within the QGIS Distance Matrix Tool.

The image shows the difference in table layout. As you can see the distances are identical, so the difference is only in the presentation of the data in the table.

The option is available at least from QGIS 2.0 onwards (haven't got any older versions available to check further back right now).

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[GIS] Distance Matrix output

If you don't mind a programmatic solution, you can do this easily in R with the dist function and the raster library. Example:

# make sure you have the raster library - you might also need rgdal
install.packages(c('raster', 'rgdal'))

# load the raster library
library(raster)

# define file path
shpFile <- "C:/path/to/shape/file.shp"

# load shapefile
shp <- shapefile(shpFile)

# convert SpatialPointsDataFrame to data.frame
shpDF <- as.data.frame(shp)

# get the distance matrix for coordinate sets
distMat <- dist(shpDF[,2:3])

# print results
print(distMat)

          1         2         3
2 192801.33                    
3 261837.21 133653.67          
4 240095.52  60905.06  86724.96

By default it will return the euclidean distance between each point in the shapefile. This should be used for data in a projected coordinate system. If you are using a geographic coordinate system, then look into the distHaversine function in the geosphere library.

QGIS Distance Matrix – Generate Line Geometry Output

As you have Distance matrix output, use its InputID and TargetID fields to build connecting lines.

Just open the Layer properties | Symbology and select Geometry generator.

If your original point layer name is points and it has id field (the one you used to create the Distance matrix), the expression would be:

make_line(geometry(get_feature('points', 'id', "InputID")), 
          geometry(get_feature('points', 'id', "TargetID")))

It will give you these connecting lines:

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[GIS] Distance Matrix output

QGIS Distance Matrix – Generate Line Geometry Output

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