I try to get sum of food produce on district but only districts with terrainTagIndustry.

I use this syntax :

$SumProperty(ClassCity,TerrainTagIndustry:DistrictFood)

Here I'm not sure there is a filter on terrain tag of the city, or if it use something else

Maybe the good one could be also :

$SumProperty(ClassCity/TerrainTagIndustry:DistrictFood)

(but as districtFood isn't a property of TerrainTag objects I'm not sure it work)

Could be also something else. I didn't find examples in vanilla game.

So it's more something to understand with good knowledge of simulations paths, and here, i don't always understand what means things when starting to use ",".