It's possible that we're looking at different data sets. I downloaded the "OS Terrain 50" "ASCII Grid and GML (Grid)" data from https://www.ordnancesurvey.co.uk/ope.../products.html and (approximately) followed Getting started with OS Terrain 50 elevation data to convert the data to a single HF2 file. The images below are from that data set (you'll need to view at full res to see the effects because they are usually ten pixels or so across and the thumbnails have been downsampled during post creation).
Is an example of facets in the data, usually caused by interpolation of vectors or overly sparse data samples.
Shows some smooth areas and facets, along with the sort of noise that I would expect from electronic collection just ofshore in the south. Areas with rapidly-changing surfaces with respect to a radar or lidar will get this very high frequency noise because the detected maximum shifts from pule to pulse in the sensor. Trees, for example, may give maximum return from their upper canopy, mid-canopy, or even ground, depending on the geometry and type of sensor.
Shows a smooth set of mountains in between two other sets. It's quite possible that the terrain really does look like this, but I'm a little suspicious about radically different characteristics in a small span.
Is the same as the previous terrain set, but shaded according to the facing angle of the terrain without regard to slope. Higher-frequency elements will show up as more broken areas in this map. The mountains in the center are very smooth, which is quite possible if they are nice rounded terrain in the midst of more broken terrain.
SRTM data is available at 1km and 90m worldwide (30m in the US, to help foreign powers with flying their terrain-following cruise missiles right to high-value targets). GLCF: Shuttle Radar Topography Mission has the basic description of the SRTM data. The original sets had holes and didn't like steep mountains or flat waterways, but they have been reprocessed a number of times in the last 13 years and merged with other high-quality data sets to give much cleaner results.
Amusingly enough, OS Terrain 50 | Business and government | Ordnance Survey describes the data as "Vector".
Please note that I'm saying that the data has no value. I'm just not sure what it offers over the SRTM product and derivatives if the data quality isn't validated. The map is no doubt 50 meters in places, but I can't tell by looking at the data which places are 50m and which are lower.
The 1970s to 1980s comment turns out to be an error on my part. I must have twitched and scrolled down half a page, because the Land-Form PANORAMA(R) entry right below the OS Terrain 50 data has that notation.
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