<!-- Stormworld Extra Terrain -->
<BarredTerrain>ArcticTerrain_rivermod</BarredTerrain>
<BarredTerrain>ArcticTerrain_Forest</BarredTerrain>
<BarredTerrain>ArcticTerrain_rivermod_proximity_poisonriver</BarredTerrain>
<BarredTerrain>ArcticTerrain_rivermod_proximity_deathriver</BarredTerrain>
<BarredTerrain>BurningLands_Rivermod</BarredTerrain>
<BarredTerrain>BurningLands_Forest</BarredTerrain>
<BarredTerrain>BurningLands_Rivermod_proximity_magmariver</BarredTerrain> <BarredTerrain>BurningLands_Rivermod_proximity_bloodriver</BarredTerrain>
<!-- End of Stormworld Extra Terrain -->  

<BarredTerrain>Land</BarredTerrain>
<BarredTerrain>Rugged_Land</BarredTerrain>
<BarredTerrain>Fertile_Land</BarredTerrain>
<BarredTerrain>DesertTerrain</BarredTerrain>
<BarredTerrain>HillsTerrain</BarredTerrain>
<BarredTerrain>ArcticTerrain</BarredTerrain>
<BarredTerrain>River</BarredTerrain>
<BarredTerrain>BurningLands</BarredTerrain>
<BarredTerrain>Fissure</BarredTerrain>
<BarredTerrain>CurgensTomb</BarredTerrain>
<BarredTerrain>Imperium</BarredTerrain>
<BarredTerrain>Scrapyard</BarredTerrain>
<BarredTerrain>Unkown</BarredTerrain>
<BarredTerrain>Tomb</BarredTerrain>

 <PreferredTerrain>Category:Land</PreferredTerrain>
<PreferredTerrain>SwampTerrain</PreferredTerrain>

Here is the code for the terrain placement of either of these props. I don't know what I'm missing... Ahh... it might be the city terrain.

<BarredTerrain>City</BarredTerrain>

That might be the error that you are seeing.. I'll check it out.

Edit: Nope.. it was just the mispelling of arctic that was causing your problems.

It should be fixed. But I don't play stormworld enough to test it appropriately

Having played with this a little bit I think it's too strong of an improvement.  No research required, just snake towards some swamps for great benefits.  Maybe tune them down to +1, with an upgradable building for +2.