3

I have created a 1km * 1km grid in QGIS using the MMQGIS plugin and below is a sample of shp@data and the layer

example1

example2

Is there a way to do a spatial join on the grid created?

I assume some grids should have more individual points (lat/long) and some should have no point data within them. I want to be able to identify the "grid_id" and the points present in the polygon such that I can then join the individual point data like below for e.g. in the below-aggregated data, which grid number does the lat and long belong to head(b)

Lat                Long     Num.CT   Num.SuccessCT Num.FailedCT Failure.rate
49.91222         -6.302522      1             1            0       0     
49.91251         -6.299382      1             1            0       0      
49.91440         -6.315690      1             1            0       0    
49.91443         -6.309872      1             1            0       0   
49.91501         -6.311369      1             0            1       1  
49.91502         -6.310905      1             1            0       0 

I tried joining the shapefile with the aggregated data. However, I can't get my head around how to plot and how would leaflet package in R identify the square

Spatial_join_by_location shapefile join aggregated data

example3

Output post joining the point layer and polygon layer

enter image description here

  • Hi, and welcome to GIS SE! – RafDouglas May 29 at 7:18
2

As I understand it, you are requesting two separate issues:

  1. how to associate each point with the ID of the tile it falls in
  2. how to count/perform stats on the points contained in each tile

Associate each point with the ID of the tile it falls in

Toolbox -> Join attribute by location

  • Input layer: choose the point layer
  • Overlay layer: choose the grid (of course it must by a polygon grid, i.e. each tile must define an area)
  • select contained as Geometric predicate (you want to associate each point with the grid tile they are contained in)

Join attribute by location

A new point layer is created, with the containing tile fields (including the IDs, in this case id_2) as added attributes:

enter image description here

You can then use id_2 to do the joins and calculations in R.

Count/perform stats on the points contained in each tile

Toolbox -> Join attributes by location (summary)

In this case you want to count how many points are contained in each tile, and have the stats calculated for you:

Join attributes by location (summary)

  • 1
    Many thanks for this , But some how i don't get an id field post joining within point layer and polygon grid layer. I have attached a snapshot of join outcome Can you help me with interpreting it correctly. I want to be able to say grid 1 - points that fall in it. What i see at the moment ( correct me if wrong ) .. Each lat /long fall in which polygon however each polygon doesnt have an id. So similar left/bottom/right/top should be labelled as GRID -1 .... – EricA May 29 at 8:31
  • I see, probably the original grid does not have an ID? In the second screenshot of your question there are only 4 fields (left bottom, right, top). If an unique ID field is missing, create it, and then re-run the join. – RafDouglas May 29 at 8:37
  • @I created the orignal grid as - Upload the CSV file with my lat/long information - create a grid layer on top - Create MMQGIS grid - X=0.1Y=0.1 unit = layer_units , Layer extent the same as lat /long in my file and saved it as shape file. I check now and the grid file created has only left , right, bottom ,top and no id , Can you suggest any other way to create an id label in my custom aggregated dataset – EricA May 29 at 8:42
  • Does each latitude and longitude gets a unique id ? I can label them in numeric column. But when there are multiple lat/long having the same co-ordinates how should i deal with labelling them – EricA May 29 at 8:43
  • 2
    make a new field (integer data type) and fill it with @row_number – Taras May 29 at 8:44

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