Index: source/gui/ObjectTypes/CMiniMap.cpp
===================================================================
--- source/gui/ObjectTypes/CMiniMap.cpp
+++ source/gui/ObjectTypes/CMiniMap.cpp
@@ -37,6 +37,7 @@
 #include "lib/external_libraries/libsdl.h"
 #include "lib/ogl.h"
 #include "lib/timer.h"
+#include "maths/MathUtil.h"
 #include "ps/CLogger.h"
 #include "ps/ConfigDB.h"
 #include "ps/CStrInternStatic.h"
@@ -345,19 +346,36 @@
 //  which represents the view of the camera in the world.
 void CMiniMap::DrawViewRect(const CMatrix3D& transform) const
 {
-	// Compute the camera frustum intersected with a fixed-height plane.
-	// Use the water height as a fixed base height, which should be the lowest we can go
-	float h = g_Renderer.GetWaterManager()->m_WaterHeight;
+	// Compute the camera frustum intersected with an imaginary plane derived from the
+	// average height of terrain in view, or the height of water, whichever is higher.
+
 	const float width = m_CachedActualSize.GetWidth();
 	const float height = m_CachedActualSize.GetHeight();
 	const float invTileMapSize = 1.0f / float(TERRAIN_TILE_SIZE * m_MapSize);
 
 	const CCamera* camera = g_Game->GetView()->GetCamera();
+	const CVector3D cameraFocus = camera->GetFocus();
+	const CVector3D cameraPosition = camera->GetOrientation().GetTranslation();
+	const CVector3D cameraDirection = camera->GetOrientation().GetIn();
+	const float cameraDistanceToFocus = cameraPosition.Y - cameraFocus.Y;
+	const float focusDiameter = sqrtf(SQR(cameraDirection.X) + SQR(cameraDirection.Z)) * cameraDistanceToFocus;
+
+	const float groundOrWaterHeight = std::max(
+		g_Game->GetWorld()->GetTerrain()->GetFilteredGroundLevel(
+			cameraFocus.X,
+			cameraFocus.Z,
+			focusDiameter / 2.f
+		),
+		g_Renderer.GetWaterManager()->m_WaterHeight
+	);
+
+	const int viewHeight = g_Renderer.GetHeight();
+	const int viewWidth = g_Renderer.GetWidth();
 	const std::array<CVector3D, 4> hitPoints = {
-		camera->GetWorldCoordinates(0, g_Renderer.GetHeight(), h),
-		camera->GetWorldCoordinates(g_Renderer.GetWidth(), g_Renderer.GetHeight(), h),
-		camera->GetWorldCoordinates(g_Renderer.GetWidth(), 0, h),
-		camera->GetWorldCoordinates(0, 0, h)
+		camera->GetWorldCoordinates(0, viewHeight, groundOrWaterHeight),
+		camera->GetWorldCoordinates(viewWidth, viewHeight, groundOrWaterHeight),
+		camera->GetWorldCoordinates(viewWidth, 0, groundOrWaterHeight),
+		camera->GetWorldCoordinates(0, 0, groundOrWaterHeight)
 	};
 
 	std::vector<CVector3D> lines;