Land of a Thousand Pools

Bosanski · In English ↓

Minnesota je zemlja deset hiljada jezera, Bosna je zemlja hiljadu rijeka, a Mostar je, kako se ispostavilo, zemlja od otprilike dvije hiljade bazena, uglavnom privatnih i nigdje registrovanih. OpenStreetMap zna za nekolicinu, a niko nije prebrojao ostale, jer prebrojati ih znači pregledati 1.143 km² krša, krov po krov.

U Mostar dolazim svake godine već petnaest godina. Vidio sam iz prve ruke koliki je napredak napravljen (ekonomski, društveni, kakav god želite), ali jedna stvar je bila očigledna: nagli porast broja izgrađenih bazena, koje domaćini obično nude dnevnim posjetiocima preko stranica kao što su booking.com i OLX. Vađenje dozvole je vrlo komplikovan proces, pa je većina njih napravljena bez nje. Povremeno primijetite i zabrinutog domaćina koji je povukao svoj oglas sa booking.com-a jer je čuo da neki radoznali službenik koristi platforme za rezervacije da postavi pitanja o neplaćenim porezima, ili tako nešto… Prošlog ljeta bilo je povremenih problema sa niskim pritiskom vode i kratkotrajnih restrikcija.

→ Otvori kartu · in English

Karta prikazuje svih 1.998 pronađenih bazena na satelitskim snimcima, grupisanih kada se odzumira; tabela dijeli broj po 115 naselja.

Postupak ima dva koraka:

1. Tlocrti zgrada iz Microsoftovog globalnog sloja svode područje pretrage na 12% općine, uz pretpostavku da se bazeni nalaze blizu kuća. Filter boje i oblika preko 20.619 Mapbox pločica rezolucije 0,217 m/piksel predlaže 4.295 kandidata.
2. ResNet-18, dodatno treniran na 600 ručno označenih isječaka, zatim odvaja bazene od plavih cerada, plavog krovnog lima i rezervoara za vodu koji zavaraju sam filter boje.

Broj koji vrijedi navesti nije 1.998. Mjereno na 200 ručno provjerenih detekcija, preciznost je 0,83, a na četiri temeljito ručno prebrojana područja odziv je 0,94. To korigovanu procjenu smješta na 1.763 bazena, vjerovatno između 1.550 i 2.481. Dva dodatna područja izvan zone pretrage prebrojana su ručno i u njima nije bilo nijednog bazena, što je jedini dokaz da je izostavljanje 88% općine bilo sigurno.

Kod i metod u repozitoriju hnk-pools. Srodni projekat: izvještaj o bosanskoj elektroenergetskoj mreži.

In English

Minnesota is the land of ten thousand lakes, Bosnia is the land of a thousand rivers, and Mostar, as it turns out, is the land of roughly two thousand pools, mostly private and registered nowhere. OpenStreetMap knows about a handful, and nobody has counted the rest, because counting them means looking at 1,143 km² of karst one rooftop at a time.

I have been coming to Mostar every year for the past fifteen years. I have seen first-hand how much progress has been made (economic, social, you name it), but one thing was obvious: the sheer increase in the number of pools being built, usually offered to day visitors on sites like booking.com and OLX. Pulling a permit is a cumbersome process, so most were built without one. Occasionally you will notice a worried host who has pulled his listing from booking.com, because he heard that some curious bureaucrat is using the booking platforms to raise questions about unpaid tax bills, or something of that sort… Last summer there were sporadic problems with low water pressure and short-term water restrictions.

→ Open the map · na bosanskom

The map plots all 1,998 detections over satellite imagery, clustered as you zoom out; the table breaks the count down across 115 settlements.

The pipeline runs in two stages:

1. Building footprints from Microsoft’s global layer prune the search area to 12% of the municipality, on the assumption that pools sit near houses. A colour and shape filter over 20,619 Mapbox tiles at 0.217 m/pixel proposes 4,295 candidates.
2. A ResNet-18, fine-tuned on 600 hand-labelled crops, then separates the pools from the blue tarpaulins, blue roof sheeting and water tanks that fool the colour filter on its own.

The number worth quoting is not 1,998. Measured against 200 hand-checked detections the precision is 0.83, and against four exhaustively hand-counted blocks the recall is 0.94. That puts the corrected estimate at 1,763 pools, plausibly between 1,550 and 2,481. Two further blocks outside the search area were hand-counted and came back empty, which is the only evidence that discarding 88% of the municipality was safe.

Code and method in the hnk-pools repository. A companion project to the Bosnian grid report.