Hello guys 

I have this problem when trying to render the map of separate regions of Italy, instead of the whole country. The problem is when there is a lake across the boundary line (it happens often in Italy).
If I process the whole country, the lakes are rendered correctly, like in this picture:

 

(This is Lago Maggiore, between Piemonte and Lombardia regions, north of Italy) 

 

If I render each region separately, the lake is not rendered correctly. For example, rendering Lombardia I get this (picture from Basecamp) :

The left part is not rendered because it’s another region (Piemonte) and this is ok.
But also the lake is rendered completely wrong: only the south part has water (near Arona city) and in the north area the water is not rendered. 

If I create the map of Piemonte, I have the same problem but with different rendering errors. I see no water on the north and water covering a part of the land in center-right:

 

 

Data of regions are downloaded from: http://download.openstreetmap.fr/extracts/europe/italy/ 

 

This is my SPLITTER configuration: 

Splitter version 653 compiled 2022-12-27T06:20:39+0000 

boundary-tags=use-exclude-list 

cache= 

description= 

geonames-file= 

handle-element-version=remove 

ignore-osm-bounds=false 

keep-complete=true 

mapid=13224200 

max-areas=2048 

max-nodes=1600000 

max-threads=16 (auto) 

mixed=false 

no-trim=false 

num-tiles= 

output=o5m 

output-dir=C:\OSM\splitter\PIEMONTE 

overlap=auto 

polygon-desc-file= 

polygon-file=C:\OSM\areas_poly\regioni\PIEMONTE.poly 

precomp-sea= 

problem-file= 

problem-report= 

resolution=13 

route-rel-values= 

search-limit=200000 

split-file= 

status-freq=120 

stop-after=dist 

wanted-admin-level=5 

write-kml= 

Elapsed time: 0s   Memory: Current 248MB (4MB used, 244MB free) Max 16384MB 

Time started: Mon Mar 13 10:18:10 CET 2023 

Map is being split for resolution 13: 

 - area boundaries are aligned to 0x800 map units (0.0439453125 degrees) 

 - areas are multiples of 0x800 map units wide and high 

 

 

These are some errors I see in Splitter log: 

Warning: Incomplete multipolygon relation 11758 (Lago Maggiore): using bbox of unclosed polygon to calc tiles, ways: [225950136, 123006579, 1073823032, 1073823028, 190504960, 87660763, 139898093, 87660754, 87660747, 255065025, 255065026, 255065027, 202250553, 202250554, 202252112, 256006208, 256006217, 256006211, 256006196, 202273125, 87660744, 87660769, 265419850, 265419849, 196817044, 202274997, 202274999, 202275000, 202274990, 202274996, 202274993, 196817042, 263324120, 263327661, 263327665, 263324123, 265406984, 265406978, 316366060, 269138792, 269138799, 87660748, 269138796, 269138795, 87660742, 87660761, 198918369, 184747058, 184747048, 87660750, 87660757, 187360834, 87660752, 87660746, 193114167, 187361863, 87660743, 87660756, 87893267, 87893275, 87893277, 814891333, 814891342, 814891332, 814891348] 

Warning: Incomplete multipolygon relation 11758 (Lago Maggiore): using bbox of unclosed polygon to calc tiles, ways: [339499330, 339499338, 339499332, 339499337, 339499331] 

Warning: Incomplete multipolygon relation 11758 (Lago Maggiore): using bbox of unclosed polygon to calc tiles, ways: [173660449, 203517579, 203517587, 173660454] 

Warning: Incomplete multipolygon relation 11758 (Lago Maggiore): using bbox of unclosed polygon to calc tiles, ways: [211154423, 211154912, 366067218, 366067212, 366067214, 366067220, 366067216, 366067222] 

Warning: Incomplete multipolygon relation 11758 (Lago Maggiore): using bbox of unclosed polygon to calc tiles, ways: [202421534, 202421531] 

Warning: Incomplete multipolygon relation 11758 (Lago Maggiore): using bbox of unclosed polygon to calc tiles, ways: [202421542, 202421532, 87896545] 

Warning: Incomplete multipolygon relation 11758 (Lago Maggiore): using bbox of unclosed polygon to calc tiles, ways: [222482940] 

Warning: Incomplete multipolygon relation 11758 (Lago Maggiore): using bbox of unclosed polygon to calc tiles, ways: [222484904, 87896544, 87894927, 222496706, 222496701, 87894916, 87894926] 

Warning: Incomplete multipolygon relation 11758 (Lago Maggiore): using bbox of unclosed polygon to calc tiles, ways: [87893287, 186266917, 186266942, 87893262, 814465684] 

 

I took a look at OpenStreetMap but I really can’t understand if there is a problem with data and multipolygons. 

Do you have any idea of how I could solve this problem ? 

Thank you !
Diego