For our analysis we used a GIS dataset on the spread of reported sightings and
removals of Hogweed and Ragweed, collected through crowdsourcing and municipal
services [10]. Covering the last 20 years, the resulting map paints the picture
of a city under siege, with sightings covering all of Zurich. Interact with the
map to find out more about locations and dates of reported sightings!
However, data visualisation can sometimes be misleading. Many of the recent
datapoints are historical and were removed already. Furthermore, the
crowdsourced nature of parts of the data leads to errors due to
misidentification of species. We reached out to GSZ to verify our findings. The
GSZ spokesperson we talked to, claimed that many of these entries are incorrect,
with only three known current locations of Common Ragweed and none for Giant
Hogweed. Our map supposedly draws a worse picture than reality.
However, GSZ only polices public spaces. Analysing the habitat distribution
showed that the most common locations for both species are private, domestic
gardens. Therefore, it is possible that the number of plants is higher than GSZ
estimates. We have to keep in mind though, that the data could be prone to a
large error, since all reports from private properties will be crowdsourced.
This creates a unique challenge for the city. While the occurrence of both
species in public areas is well documented, their presence remains uncertain on
private land. The city must rely on awareness campaigns and the common sense of
its citizens to fight their spread on private property.
