Adding up data values from different vector layers

Question

I have multiple files each loaded as a layer. Each file has just an easting northing and a count value, as below.

easting,northing,count
435575,804275,15
435625,804225,29
435625,804275,39
435625,804325,53
435675,804075,8
435675,804125,11
435675,804175,45
435675,804225,60
435675,804275,81
435675,804325,117
435675,804375,83
435725,804025,16
435725,804075,21
435725,804125,64
435725,804175,76
435725,804225,113

All the easting and northing points are on the same 50m x 50m grid.

I have used the count value to colorize this data, selecting a 50m square though the geometry manager which looks good for each layer in isolation.

What I can't work out how to do is :

These layers overlap each other. Where they overlap each other I would like to sum the count from each point at the same easting and northing position, to produce a single data set.

Answer 1

1. vector > Geoprocessing Tools > intersect - gets you the overlap area
2. vector > data management tools > join attribute by location - joins your point data to the intersect layer
3. use field calculator to sum all the count attributes into a new field

Answer 2

Since your layers are points dataset, intersect may not work. If so, please try a workflow below.

(1) Your data

I imported your sample as points1 layer (green), and chose last 3 points of your data as the overlapping points2 layer (orange)...[LHS] These layers can be displayed as if tiles (50m x 50m square symbols), but they are point layers... [RHS image]

(2) Add up 2 layers

There would be various approaches, but I used refFunctions plugin this time, which provides geomequals() function to overlay point-point layers.

(2 - 1) Extract count data from point2 layer.

1. Open attribute table of point1 layer and create a new count_2 field
2. Expression is geomequals( 'points2', 'count')

(2 - 2) Add count and count_2 fields.

1. Create a new my_sum field
2. Expression is "count" + coalesce("count_2",0)

(3) Visualize my_sum field