I guess the tile doesn't *have* to be flattened, since the graphic painter would simply paint something that looks like it should fit on a sloped tile... I was just thinking that they might paint something that looks like a box, or concrete slope with integrated pillar...
AEO's mockup is nice, though not quite what I was thinking - instead of just doing the pillar down there, I was thinking of either a concrete box to "flatten" it upward (but Simutrans has to flatten downward so you can draw a box), or perhaps a replacement for the sloped tile, but concrete on a slope...
http://i.imgur.com/aqsPt.jpg - I can't find a better image offhand... but the concrete is sort of on a 'slope-tile' there, even though there's no pillar on it.... So like it could be painted to be concrete on the grass, with a pillar base coming up from that or something...
I guess painters would have the best ideas on how to do this. I just was trying to come up with some way of alleviating how a pillar placed on a slope tile looks *wrong* in the game. heh.
So, better ideas ahoy!

Why even flatten the pillar tile? There could be 6 possible foundations - flat, water and slopes. (The non-straight slopes are something of a nuisance, yeah...) For top of pillar, I'd go for changing the "way" tile instead of pillar, since that gives more graphical possibilities.
I love that idea - different foundations for water, in particular. Glad I posted this just for that idea!
