Index: ps/trunk/binaries/data/mods/public/globalscripts/Trade.js
===================================================================
--- ps/trunk/binaries/data/mods/public/globalscripts/Trade.js
+++ ps/trunk/binaries/data/mods/public/globalscripts/Trade.js
@@ -0,0 +1,15 @@
+/**
+ * Normalize the trade gain as a function of mapSize, default=1024
+ */
+function TradeGainNormalization(mapSize)
+{
+	return 1;
+}
+
+/**
+ * Dependance of the gain with distance, normalized on a distance of 100m
+ */
+function NormalizedTradeGain(distanceSquared)
+{
+	return distanceSquared / 10000;
+}
Index: ps/trunk/binaries/data/mods/public/simulation/ai/common-api/gamestate.js
===================================================================
--- ps/trunk/binaries/data/mods/public/simulation/ai/common-api/gamestate.js
+++ ps/trunk/binaries/data/mods/public/simulation/ai/common-api/gamestate.js
@@ -936,10 +936,13 @@
 	let supportTraderTemplateName = this.applyCiv("units/{civ}_support_trader");
 	let shipMerchantTemplate = !this.isTemplateDisabled(shipMechantTemplateName) && this.getTemplate(shipMechantTemplateName);
 	let supportTraderTemplate = !this.isTemplateDisabled(supportTraderTemplateName) && this.getTemplate(supportTraderTemplateName);
-	return {
-		"navalGainMultiplier": shipMerchantTemplate && shipMerchantTemplate.gainMultiplier(),
-		"landGainMultiplier": supportTraderTemplate && supportTraderTemplate.gainMultiplier()
-	};
+	let norm = TradeGainNormalization(this.sharedScript.mapSize);
+	let ret = {};
+	if (supportTraderTemplate)
+		ret.landGainMultiplier = norm * supportTraderTemplate.gainMultiplier();
+	if (shipMerchantTemplate)
+		ret.navalGainMultiplier = norm * shipMerchantTemplate.gainMultiplier();
+	return ret;
 };
 
 return m;
Index: ps/trunk/binaries/data/mods/public/simulation/ai/petra/headquarters.js
===================================================================
--- ps/trunk/binaries/data/mods/public/simulation/ai/petra/headquarters.js
+++ ps/trunk/binaries/data/mods/public/simulation/ai/petra/headquarters.js
@@ -1104,8 +1104,9 @@
 /**
  * Returns the best position to build a new market: if the allies already have a market, build it as far as possible
  * from it, although not in our border to be able to defend it easily. If no allied market, our second market will
- * follow the same logic
- * TODO check that it is on same accessIndex
+ * follow the same logic.
+ * To do so, we suppose that the gain/distance is an increasing function of distance and look for the max distance
+ * for performance reasons.
  */
 m.HQ.prototype.findMarketLocation = function(gameState, template)
 {
@@ -1127,6 +1128,8 @@
 	let bestIdx;
 	let bestJdx;
 	let bestVal;
+	let bestDistSq;
+	let bestGainMult;
 	let radius = Math.ceil(template.obstructionRadius().max / obstructions.cellSize);
 	let isNavalMarket = template.hasClass("NavalMarket");
 
@@ -1152,6 +1155,8 @@
 		let pos = [cellSize * (j%width+0.5), cellSize * (Math.floor(j/width)+0.5)];
 		// checking distances to other markets
 		let maxVal = 0;
+		let maxDistSq;
+		let maxGainMult;
 		let gainMultiplier;
 		for (let market of markets)
 		{
@@ -1168,9 +1173,13 @@
 				continue;
 			if (!gainMultiplier)
 				continue;
-			let val = API3.SquareVectorDistance(market.position(), pos) * gainMultiplier;
-			if (val > maxVal)
-				maxVal = val;
+			let distSq = API3.SquareVectorDistance(market.position(), pos);
+			if (gainMultiplier * distSq > maxVal)
+			{
+				maxVal = gainMultiplier * distSq;
+				maxDistSq = distSq;
+				maxGainMult = gainMultiplier;
+			}
 		}
 		if (maxVal === 0)
 			continue;
@@ -1179,6 +1188,8 @@
 		if (this.isDangerousLocation(gameState, pos, halfSize))
 			continue;
 		bestVal = maxVal;
+		bestDistSq = maxDistSq;
+		bestGainMult = maxGainMult;
 		bestIdx = i;
 		bestJdx = j;
 	}
@@ -1188,7 +1199,7 @@
 
 	if (bestVal === undefined)  // no constraints. For the time being, place it arbitrarily by the ConstructionPlan
 		return [-1, -1, -1, 0];
-	let expectedGain = Math.round(bestVal / 10000);
+	let expectedGain = Math.round(bestGainMult * NormalizedTradeGain(bestDistSq));
 	if (this.Config.debug > 1)
 		API3.warn("this would give a trading gain of " + expectedGain);
 	// do not keep it if gain is too small, except if this is our first BarterMarket
Index: ps/trunk/binaries/data/mods/public/simulation/ai/petra/tradeManager.js
===================================================================
--- ps/trunk/binaries/data/mods/public/simulation/ai/petra/tradeManager.js
+++ ps/trunk/binaries/data/mods/public/simulation/ai/petra/tradeManager.js
@@ -444,7 +444,7 @@
 				gainMultiplier = traderTemplatesGains.navalGainMultiplier;
 			else
 				continue;
-			let gain = Math.round(API3.SquareVectorDistance(m1.position(), m2.position()) * gainMultiplier / 10000);
+			let gain = Math.round(gainMultiplier * NormalizedTradeGain(API3.SquareVectorDistance(m1.position(), m2.position())));
 			if (gain < this.minimalGain)
 				continue;
 			if (m1.foundationProgress() === undefined && m2.foundationProgress() === undefined)
Index: ps/trunk/binaries/data/mods/public/simulation/components/Trader.js
===================================================================
--- ps/trunk/binaries/data/mods/public/simulation/components/Trader.js
+++ ps/trunk/binaries/data/mods/public/simulation/components/Trader.js
@@ -11,7 +11,7 @@
 	"<a:example>" +
 		"<GainMultiplier>0.75</GainMultiplier>" +
 	"</a:example>" +
-	"<element name='GainMultiplier' a:help='Trader gain for a 100m distance'>" +
+	"<element name='GainMultiplier' a:help='Trader gain for a 100m distance and mapSize = 1024'>" +
 		"<ref name='positiveDecimal'/>" +
 	"</element>";
 
Index: ps/trunk/binaries/data/mods/public/simulation/helpers/TraderGain.js
===================================================================
--- ps/trunk/binaries/data/mods/public/simulation/helpers/TraderGain.js
+++ ps/trunk/binaries/data/mods/public/simulation/helpers/TraderGain.js
@@ -18,19 +18,19 @@
 	let firstMarketPosition = cmpFirstMarketPosition.GetPosition2D();
 	let secondMarketPosition = cmpSecondMarketPosition.GetPosition2D();
 
-	let gainMultiplier;
+	let gainMultiplier = TradeGainNormalization(Engine.QueryInterface(SYSTEM_ENTITY, IID_Terrain).GetMapSize());
 	if (trader)
 	{
 		let cmpTrader = Engine.QueryInterface(trader, IID_Trader);
 		if (!cmpTrader)
 			return null;
-		gainMultiplier = cmpTrader.GetTraderGainMultiplier();
+		gainMultiplier *= cmpTrader.GetTraderGainMultiplier();
 	}
 	else	//called from the gui, modifications already applied
 	{
 		if (!traderTemplate || !traderTemplate.GainMultiplier)
 			return null;
-		gainMultiplier = traderTemplate.GainMultiplier;
+		gainMultiplier *= traderTemplate.GainMultiplier;
 	}
 
 	let gain = {};
@@ -40,7 +40,7 @@
 	let distanceSq = firstMarketPosition.distanceToSquared(secondMarketPosition);
 	// We calculate gain as square of distance to encourage trading between remote markets
 	// and gainMultiplier corresponds to the gain for a 100m distance
-	gain.traderGain = gainMultiplier * distanceSq / 10000;
+	gain.traderGain = gainMultiplier * NormalizedTradeGain(distanceSq);
 
 	gain.market1Owner = cmpMarket1Player.GetPlayerID();
 	gain.market2Owner = cmpMarket2Player.GetPlayerID();