A while back I compared three sites that crowdsource data about the natural world: the RSPB’s Big Garden Birdwatch, NatureLocator’s Leaf Watch and the UK snow map. I return to these sites and consider another aspect: geographical unevenness.
(Leaf Watch has I think ended but other NatureLocator surveys have been running and the same principles apply to them).
All these sites ask people to submit information about what is visible around them. So you are likely to get more reports from where there are many people, such as big cities and fewer from sparsely inhabited areas such as the Highlands or mid-Wales.
For the snow map this may not matter too much. It’s clear there are people in remote areas sending in reports, which appear as dots or flakes on the map. There are some in the ‘cefn gwlad’ behind Aberystwyth as I write. And there appears to be a limit on how many dots can appear in the same small area. Nevertheless, snowfall in London generates a busier looking map than snowfall in the countryside. But the snow map is not a matter of record; it is ephemeral and serves to inform people right now about where snow is falling so they can plan journeys/get the sledge out/feel Schadenfreude. So, when looking at it, it just needs a little thought and a mental map of major centres of population to factor out the weighting towards cities.
The Big Garden Birdwatch does not attempt to cover the country evenly. It’s expected that the birdwatching will take place in gardens (hence the name) or public parks, and the survey is specifically intended to measure avian activity near human settlements. (This will cause variations, for example due to hard weather in some years which will drive birds from open country into gardens. There are further sources of bias, for example caused by one species of bird being mistaken for another and by less conspicuous species such as wrens being undercounted. And being in January summer visitors will be missed altogether. But that’s going beyond the scope of this post.)
NatureLocator is a scientific project which was driven by biologists needing data. Although it was produced by colleagues, I haven’t been involved enough to know what exactly is done with the information submitted. Since what was being measured was the overall distribution of leaf miner moth infestation and the proportion of trees affected, the main risk due to geographical unevenness is not getting enough reports in some areas. There might also be a bias due to users being more likely to report the presence of the moth than its absence. The results are summarised here where the geographical issue is acknowledged.