So after finally getting around to writing another blog post over the weekend, it’s time to get really stuck into things as we enter #TipWeek at the Data School.
First up, a simple tip that I picked up from Alteryx ACE, Tableau Zen Master and all round top guy, Chris Love on how to deal with Eastings and Northings. A form of grid reference, Easting refers to an eastward-measured distance (equivalent to the x co-ordinate), while northing refers to a northward-measured distance (the y-coordinate).
If you encounter a dataset with geographic data referring to Eastings and Northings, such as London road traffic accident data, simply fire up Alteryx and read in your data. From here, we can use the spatial data tool ‘Create Points’ to generate a point on a map (known as a Centroid) and we can then download and use the very handy Information Lab macro to convert the centroid into a polygon with associated latitude and longitude points.
Simply drag and drop the Create Points tool into your workflow, select your Eastings data in the X field, Northings in the Y field and then select the ‘Fields are Projected Floating Points’ field where we can edit the default mapping reference.
From here, expand the ‘National Grids’ field and select the ‘British National Grid / OSGB 1936’ option.
This should then automatically populate the ‘Fields are Projected Floating Points’ field with ‘EPSG:27700’. Now drop on the newly downloaded Tableau Polygon tool and select the Centroid (SpatialObj) field.
Doing this will then create latitude and longitude fields, as well as PolygonID, PointID’s etc. for if you need to draw a more complex shape within Tableau. Output your data as necessary, connect to it in Tableau and hey presto – you can now generate a map view!
Hopefully this was all clear but feel free to comment if you have any questions or feedback. Happy Tableau-ing and be sure to check back tomorrow where I’ll show you how to convert Unix time into something you can actually understand!