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Silph Study: #043

Published:
03.17.2021

Souvenir Survey: Beach Glass and Tropical Shells

Greetings, travelers! In December 2019, the Pokémon GO buddy feature was updated, adding the ability for your favorite Ultra and Best buddies to bring souvenir items. In our previous study, we looked at the group of souvenirs which we believe are “universal” — that is, your buddy can find them anywhere. In this article, we’re examining some of the rarest souvenirs: Beach Glass and Tropical Shells. With over 14,000 souvenirs collected so far, our researchers have found a mere 28 Beach Glass and 68 Tropical Shells — a combined 0.7%! As with several other souvenirs, we suspect that these are extremely rare because your buddy can only find them in certain specific locations. (We will refer to these as “location-dependent” souvenirs.) Without further ado, let’s unpack the criteria behind where and how they can be found!

Key Findings

  • Tropical Shells can be found in areas containing the OpenStreetMap (OSM) tag natural=coastline.
  • Beach Glass can be found in areas containing the OSM tag natural=beach.
  • If available in an area, the base rarity of Beach Glass are 2.85% and the base rarity of Tropical Shells are 5.46%.

Coastline and Beach OSM Tags

Pokémon GO uses data sourced from OpenStreetMap (OSM) to build the visible overworld map. OSM data has been shown to influence many hidden features, such as biomes and nests. In our previous study on Skipping Stones, we showed that certain water-related OSM tags (such as natural=water) were a prerequisite for finding the Skipping Stone souvenir.

To examine Beach Glass and Tropical Shell souvenirs, we matched OSM tags common among the locations where they were found. Our researchers found 28 Beach Glass across 16 different locations, all of which contained a feature tagged with the key-value pair natural=beach. Likewise, 68 Tropical Shells were found across 20 locations, each of which contained an area tagged with natural=coastline. An example of one of these locations is shown below.

Image: Coastal region in Nordland, Norway with a natural=coastline OSM Tag. Of the 16 souvenirs collected, 3 were Tropical shells. Map © OpenStreetMap Contributors.

Researchers sent their buddies looking for souvenirs at locations with one or both of these tags present. Both Beach Glass and Tropical Shells were found independent of one another, with their availability triggered by their respective OSM tags. For example, the image below shows an inland river that contains a natural=beach tag without the often-associated natural=coastline tag. The researcher’s buddy found a Beach Glass, but did not find any Tropical Shells in 114 souvenirs. 

Image: A river beach found in upstate New York, USA with the natural=beach OSM Tag. In 114 souvenirs, the researcher’s buddy found a Beach Glass but did not find any Tropical Shells. Map © OpenStreetMap Contributors.

Furthermore, multiple triggering tags in the same area do not interfere with one another. In the rare instance that a cell contains beach, coastline, and water-related OSM tags, your buddy might be able to find Beach Glass, Tropical Shells, and Skipping Stones (as in the following example).

Image: An S2 cell in Southern California, USA which contains the natural=beach, natural=wetland and natural=coastline tags. In this location, 122 total souvenirs were collected including 5 Beach Glass, 6 Skipping Stones, and 10 Tropical Shells. Map © OpenStreetMap Contributors.

Necessary or Sufficient?

Of the more than 200 unique locations tested, neither Beach Glass nor Tropical Shells were found without natural=beach or natural=coastline, respectively. A multitude of compatible examples and lack of counter-examples leads us to conclude that the presence of a natural=beach or natural=coastline tag are a necessary condition in order for your buddy to find the respective souvenir. That is, we believe that your buddy can only find these souvenirs in areas with the respective OSM tag.

Researchers have yet to find Beach Glass at five unique locations with a natural=beach tag, amassing a total of 201 souvenirs. Likewise, 673 souvenirs were collected at 16 unique locations with the natural=coastline tag, with no Tropical Shells found. Determining whether these results are unexpected requires a wider view of the entire dataset. Given the number of locations sampled and the souvenirs found at each, we estimate the probability of not finding the souvenirs in at least 5 beach locations and 16 coastline locations to be 0.7962 and 0.0031, respectively.¹

Their absence so far does not guarantee that they are unavailable. As we will discuss in a later section, these souvenirs can be incredibly rare even at locations where it’s possible to find them. These results suggest, however, that there might be a second condition needed to trigger the availability of these souvenirs. That is, we cannot say with certainty that these tags are a sufficient condition. It’s possible that your buddy may not be able to bring you these souvenirs even if a location contains the tags.

Confirming the S2 Cell Level

S2 cells are an efficient method for indexing spatial data for large-scale maps. The globe is divided into smaller and smaller grid cells, creating “levels” that give spatial hierarchy. Levels with low numbers are associated with the largest grid sizes, and progressively higher numbers refer to smaller and smaller grids, with Level 30 cells being just a few centimeters across. S2 geometry is a hidden cornerstone of key game mechanics including PokéStops, Gyms, EX Raids, biomes, and much more.

In our study of Skipping Stones, we determined that your buddy only considers natural=water tags that are within the same Level 14 cell (roughly 0.33 km² or 0.12 mi²) as your avatar.

Here, we extended the test to both Beach Glass and Tropical Shells. Our researchers were able to find a souvenir as long as the associated tag was within the same Level 14 cell. If a tag lay outside of the cell, the associated souvenir was not found. In the example below, a researcher positioned themselves on the opposite side of a Level 14 S2 cell from the natural=beach tag, with a natural=coastline tag lying just outside of the cell boundary. Beach Glass was found at the yellow X but the researcher’s buddy was not able to find any Tropical Shells. Both souvenirs were found in the cell directly to the west, which contains both tags.

Image: A level 14 S2 cell in Southern California, USA which contains the natural=beach tag. The natural=coastline tag lies just outside of the cell boundary. Beach glass was found at the X, but not Tropical Shells. Map © OpenStreetMap Contributors.

Beach Glass and Tropical Shell Rarity

It is difficult to compare the rarity of Beach Glass and Tropical Shells across locations with different location-dependent souvenirs available. For example, the high rate of Snowy Pinecones in one location might mask the chance of finding Beach Glass compared to a location with no Snowy Pinecones. To control for this, we calculate the “base rate” of each souvenir as the number of Beach Glass or Tropical Shells compared to the number of universal souvenirs. The table below shows the counts and base rates across all locations with the corresponding tags.

OSM Tag Beach Glass Tropical Shells Universal Souvenirs Base Rate
natural=beach 29 987 2.85%
natural=coastline 68 1,177 5.46%

It should be stressed that the base rate is the highest estimated frequency of these souvenirs. It’s the rate that would be expected if the eight Universal souvenirs were the only other souvenirs available at that location. Most areas have access to multiple location-dependent souvenirs, so the actual probability of finding each of these souvenirs may be significantly lower. In a hypothetical cell with access to all 15 souvenirs, we estimate the chance of finding a Beach Glass would drop to less than one percent!

Parting Words

Beach Glass and Tropical Shells are highly sought-after souvenirs, but travelers should temper their expectations when attempting to obtain these from a cell containing natural=beach or natural=coastline. Some researchers have been lucky enough to obtain Beach Glass or Tropical Shells from their first few attempts, while other researchers have received nearly 200 souvenirs before finding a single Beach Glass. We cannot guarantee that either Beach Glass or Tropical Shells are found at an equal rate across all eligible locations.

Landlocked travelers may need to venture far from home to track down one of these souvenirs. However, a trip to the coast may not be necessary. Beach Glass has been found at multiple beaches on inland rivers and lakes. If you’re in search of one of these elusive souvenirs, make sure to check OpenStreetMap in your area.²

Until next time, travelers, stay safe on the Road!


Acknowledgments

Authors: Scientist CaroKann and Lead Researcher archer
Analysis: Scientists CaroKann and Titleist, and Lead Researchers archer and Sinkalingsveis
Graphics: Scientists WoodWoseWulf and CaroKann

Project Leaders: Lead Researchers Belle and Pancake
Editing: Scientists Cham1nade and skyeofthetyger
Data collection: 339 explorer-researchers collected data for this project. These nine were instrumental in determining Tropical Shell and Beach Glass criteria.

  • AlertedFancy
  • Cesca1889
  • DeeDillyDawn
  • JMcQueen81
  • Katana1013
  • Krag
  • RDC-DCIfan68
  • Reykius
  • TwitchToxin

Footnotes

¹ Using iterative simulation, we estimated the likelihood that a number of locations in our sample would not produce a souvenir due to random chance despite meeting the OSM tag criteria. For each iteration in the Beach Glass simulation, we simulated the n=21 different natural=beach locations. For each location, we simulated it producing a Beach Glass as a factor of the base rate (b=0.0285) for an m number of times, where m is the number of universal souvenirs observed at that location. The probability estimate is the number of iterations which had zero Beach Glass in 5 or more locations (7,962), divided by the total number of iterations (10,000).

Likewise, for Tropical Shells, we simulated n=36 locations at the base rate b=0.0546. The probability estimate is the number of iterations which had zero Tropical Shells in 16 or more locations (31), divided by the total number of iterations (10,000). 

² Due to Niantic’s infrequent map updates, the data presented in this article was analyzed under the assumption that location-dependent souvenir criteria are being determined using the same OSM geodata that Niantic is currently using for nests and spawn-blocking areas. At the time of this article’s publication, the most accurate source date we have for this OSM data is February 25, 2019. During the course of this study, we did not find any cases that contradict the established source date.

There is no evidence that creating new tags on OSM will have any impact on the availability of souvenirs. Further, there is no way to predict if, when, or how Niantic might update or change the geodata used in Pokémon GO. The Silph Research Group encourages newly-inspired mappers to act courteously and respectfully when it comes to OSM and their local mapping communities.