"Oh Nodes: My final research project on OSM paths and their links to the “increased rural spawns” in Pokemon Go"

#PokemonGO: This was one of those times when one starts with a hypothesis, gathers data, and then discovers something completely different and possibly even more interesting.TLDR“path spawns” are not based on nodes/points between Open Street Map path lines.Instead, they occur in small s2 cells along or (more rarely) directly adjacent to specific OSM paths.Spawns appear to always occur in the centre of level 20 s2 cells.This might give an indication of how some biomes like water work – spawns in cells within a certain distance of “mapped water” lines may have water spawns that gradually peter out or stop suddenly.Fair warning to anyone who reads this post, the first section details an experiment attempting to prove a failed hypothesis , but also contains information regarding the methods used to reach specific conclusions.HypothesisHaving spent some time experimenting with the links between specific paths marked on Open Street Map (OSM), and with other recent findings related to OSM in mind, I believe the discussion has for the most part moved past the stage of gathering evidence of correlation and instead now needs to focus on investigating method and functionality.Having communicated with a number of travelers on the topic, as well as reading the plethora of posts made by Redditors, I came to the realisation that detailed paths with many points between their lines were also more likely to have spawns added specifically by the December rural spawn increase.As such, I came to the idea that spawns would be distributed along paths by simply turning the points between individual lines into spawnpoints.Testing MethodologyLuckily I have an ideal natural laboratory very close to my home that I can run these kinds of experiments in:A state forest with many hiking trails, all of which are marked with great detail on OSM based on a single user’s GPS traces over a year ago, none of these trails show on Google Maps or Earth and never have.In all, I used a total of 4 apps: a widget to give a readout of my current GPS location, Google Maps, Maps.Me and Pokemon Go, I also used Open Street Map back at the Pokemon Lab (AKA my little house on the edge of the forest).During the process of this experiment, I followed two trails carefully and positioned my trainer avatar on top the centre of the circle of each spawn as accurately as I could, observing Maps.Me for correlations between OSM and my location and my GPS location for further research.FindingsIt rapidly became apparent that spawns do not align to OSM points between lines. But normally, each line will only have 0 to 2 spawns regardless of its size, ergo, more complex paths will often have more spawns.However:Of the 35 spawns points locations that I recorded, 33 of them still aligned perfectly to the lines between the points (including inaccuracies in the way of the trail), and 2 of them were close, but within a few metres of the path.My first inclination was that perhaps the lines marking the paths had been simplified with some nodes removed on really complex curves. I investigated further…A Second Hypothesis My focus turned to the two anomalous spawn points. Why were just under 5% of the spawns out of alignment with OSM marked paths?I thought that perhaps, in a similar method to Pokéstop spawns, path spawns were spread in a random manner around their nodes?Remembering the Pokémon Go beta, where screenshots could be seen of shimmering leaf blobs aligned in a smooth, but also grid like fashion, I had a thought and I turned back to my previous experiments with S2 Cells and how they are used to define the caught location of Pokémon.The traveler Calmarius gives a beautifully simple and almost poetic description of how S2 works here.S2 Cells and Spawn PointsI began to enter the spawn data I had recorded into S2map.After running a few different sizes of cell through the S2 grids of different sizes, I came to level 20 cells, and that’s where things became interesting. Every spawn location I entered aligned perfectly to the centre of a level 20 s2 cell. Further, while the two anomalous spawn points did not align to the paths, they were directly adjacent to cells that did.I went further an analysed multiple spawns over multiple days in different locations. Every spawn, no matter where I checked aligned to the centre of a Level 20 S2 cell.ConclusionsFirstly, I can confirm that the individual points that make up ends of OSM lines do not contribute to the distribution of spawns aside from their actual requirement to be there to create the lines which actually do appear to have influence.It seems that spawn points are organised along a 20 s2 grid, which might explain why in some busy locations Pokémon so readily overlap with each other.For reference, this is what Santa Monica looks like with S2 level 20 marked over it.Obviously it is important to note that not every cell has a spawn point. What is interesting in all of this is that through the two anomalous cells, we might see a faint glimmer of how some biomes work. The majority of cells that had spawns were directly intersected by paths, but the two that didn’t were adjacent – perhaps some kind of algorithm is in place to “fade” the spawns along the OSM lines which gives some, lesser priority to cells next to cells with the appropriate features in order to provide biome data.An observant traveler might be able to see similar effects (perhaps even more obviously over a greater space) along the edges of water or electric biomes, or perhaps they may be able to identify more stark biome boundaries along particular level s2 Cell boundaries.A Final NoteThose that are editing OSM may be tempted to add paths to increase spawns. While I encourage accurate and thoughtful edits of OSM, I have still yet to find a path that was created after Pokémon Go launched which has seen an increase in spawns. It may be that the rural spawn increase was a “one time deal” kind of situation, but only the future will reveal what can and will happen. via /r/TheSilphRoad http://ift.tt/2jD2R30