When Blockmap lump is not created?

When a map is a tad big, SRB2DoomBuilder can't create a valid Blockmap lump in the level wad; and, if I'm not wrong, this has some side effects.

My level pack has currently 7 maps, the biggest one has ~29000 FU x 29000 FU wide and it's the only one that doesn't have a blockmap lump. The 2nd one has 26000 FU x 16000 FU wide and possesses a blockmap lump though.

I'd like to know, say, which is the limit in which DB is able to create a blockmap lump.

I think the blockmap actually has a maximum size due to format specification. (Doom maps were only supposed to be so big.)

If I'm not mistaken, you should be able to just omit the blockmap from the offending maps and SRB2 will make one on the fly when you load it.

Yeah, IIRC internally-made BLOCKMAP files needn't be restricted to the WAD file format's limitations. Most source ports take advantage of this, and I'd imagine SRB2 is no exception.

If there isn't a BLOCKMAP at all, though - like, not even the game can generate one for whatever reason - then while rendering of the stage will be fine, there'll be no collision detection at all.

SRB2 has an internal blockmap generator and will do so on map load if there isn't one in the stage. In fact, it's generally suggested to delete the blockmap lump when releasing the file because the blockmap can take up a decent amount of space, especially in large level packs. SRB2's internal blockmap generator should not have any limitations, but there are limitations to other parts of the nodesbuilding process that you'll hit before you actually manage to fill a 64k by 64k square to the brim. NAGZ, for example, has no reject, which causes some collision detection errors. Zennode actually crashes outright if it attempts to make one.

If you truly must use the blockmap a nodesbuilder generates, the limit is that the blockmap cannot be larger than 128K. This is a limitation in the original Doom file format and can't really be gotten around outside of having the game generate a blockmap when loading the stage (which is what SRB2 does).