diff --git a/src/autoreplace_gui.cpp b/src/autoreplace_gui.cpp
index db58477657..f6d819d612 100644
--- a/src/autoreplace_gui.cpp
+++ b/src/autoreplace_gui.cpp
@@ -71,7 +71,6 @@ void AddRemoveEngineFromAutoreplaceAndBuildWindows(VehicleType type)
 static const StringID _start_replace_dropdown[] = {
 	STR_REPLACE_VEHICLES_NOW,
 	STR_REPLACE_VEHICLES_WHEN_OLD,
-	INVALID_STRING_ID
 };
 
 /**
diff --git a/src/bridge_gui.cpp b/src/bridge_gui.cpp
index 9683b59d33..023411b115 100644
--- a/src/bridge_gui.cpp
+++ b/src/bridge_gui.cpp
@@ -79,7 +79,6 @@ private:
 		STR_SORT_BY_NUMBER,
 		STR_SORT_BY_COST,
 		STR_SORT_BY_MAX_SPEED,
-		INVALID_STRING_ID
 	};
 	static const std::initializer_list<GUIBridgeList::SortFunction * const> sorter_funcs;
 
diff --git a/src/build_vehicle_gui.cpp b/src/build_vehicle_gui.cpp
index 6c587e794b..12934979ef 100644
--- a/src/build_vehicle_gui.cpp
+++ b/src/build_vehicle_gui.cpp
@@ -497,7 +497,6 @@ const std::initializer_list<const StringID> _engine_sort_listing[] = {{
 	STR_SORT_BY_POWER_VS_RUNNING_COST,
 	STR_SORT_BY_RELIABILITY,
 	STR_SORT_BY_CARGO_CAPACITY,
-	INVALID_STRING_ID
 }, {
 	/* Road vehicles */
 	STR_SORT_BY_ENGINE_ID,
@@ -511,7 +510,6 @@ const std::initializer_list<const StringID> _engine_sort_listing[] = {{
 	STR_SORT_BY_POWER_VS_RUNNING_COST,
 	STR_SORT_BY_RELIABILITY,
 	STR_SORT_BY_CARGO_CAPACITY,
-	INVALID_STRING_ID
 }, {
 	/* Ships */
 	STR_SORT_BY_ENGINE_ID,
@@ -522,7 +520,6 @@ const std::initializer_list<const StringID> _engine_sort_listing[] = {{
 	STR_SORT_BY_RUNNING_COST,
 	STR_SORT_BY_RELIABILITY,
 	STR_SORT_BY_CARGO_CAPACITY,
-	INVALID_STRING_ID
 }, {
 	/* Aircraft */
 	STR_SORT_BY_ENGINE_ID,
@@ -534,7 +531,6 @@ const std::initializer_list<const StringID> _engine_sort_listing[] = {{
 	STR_SORT_BY_RELIABILITY,
 	STR_SORT_BY_CARGO_CAPACITY,
 	STR_SORT_BY_RANGE,
-	INVALID_STRING_ID
 }};
 
 /** Filters vehicles by cargo and engine (in case of rail vehicle). */
diff --git a/src/dropdown.cpp b/src/dropdown.cpp
index da92a0c765..2e1cd43452 100644
--- a/src/dropdown.cpp
+++ b/src/dropdown.cpp
@@ -431,7 +431,7 @@ void ShowDropDownList(Window *w, DropDownList &&list, int selected, WidgetID but
  * Show a dropdown menu window near a widget of the parent window.
  * The result code of the items is their index in the \a strings list.
  * @param w             Parent window that wants the dropdown menu.
- * @param strings       Menu list, end with #INVALID_STRING_ID
+ * @param strings       Menu list.
  * @param selected      Index of initial selected item.
  * @param button        Button widget number of the parent window \a w that wants the dropdown menu.
  * @param disabled_mask Bitmask for disabled items (items with their bit set are displayed, but not selectable in the dropdown list).
@@ -442,10 +442,12 @@ void ShowDropDownMenu(Window *w, std::span<const StringID> strings, int selected
 {
 	DropDownList list;
 
-	for (uint i = 0; strings[i] != INVALID_STRING_ID; i++) {
+	uint i = 0;
+	for (auto string : strings) {
 		if (!HasBit(hidden_mask, i)) {
-			list.push_back(MakeDropDownListStringItem(strings[i], i, HasBit(disabled_mask, i)));
+			list.push_back(MakeDropDownListStringItem(string, i, HasBit(disabled_mask, i)));
 		}
+		++i;
 	}
 
 	if (!list.empty()) ShowDropDownList(w, std::move(list), selected, button, width);
diff --git a/src/genworld_gui.cpp b/src/genworld_gui.cpp
index 4ac2bbae36..cd203da979 100644
--- a/src/genworld_gui.cpp
+++ b/src/genworld_gui.cpp
@@ -373,16 +373,16 @@ static DropDownList BuildTownNameDropDown()
 }
 
 
-static const StringID _elevations[]  = {STR_TERRAIN_TYPE_VERY_FLAT, STR_TERRAIN_TYPE_FLAT, STR_TERRAIN_TYPE_HILLY, STR_TERRAIN_TYPE_MOUNTAINOUS, STR_TERRAIN_TYPE_ALPINIST, STR_TERRAIN_TYPE_CUSTOM, INVALID_STRING_ID};
-static const StringID _sea_lakes[]   = {STR_SEA_LEVEL_VERY_LOW, STR_SEA_LEVEL_LOW, STR_SEA_LEVEL_MEDIUM, STR_SEA_LEVEL_HIGH, STR_SEA_LEVEL_CUSTOM, INVALID_STRING_ID};
-static const StringID _rivers[]      = {STR_RIVERS_NONE, STR_RIVERS_FEW, STR_RIVERS_MODERATE, STR_RIVERS_LOT, INVALID_STRING_ID};
-static const StringID _smoothness[]  = {STR_CONFIG_SETTING_ROUGHNESS_OF_TERRAIN_VERY_SMOOTH, STR_CONFIG_SETTING_ROUGHNESS_OF_TERRAIN_SMOOTH, STR_CONFIG_SETTING_ROUGHNESS_OF_TERRAIN_ROUGH, STR_CONFIG_SETTING_ROUGHNESS_OF_TERRAIN_VERY_ROUGH, INVALID_STRING_ID};
-static const StringID _rotation[]    = {STR_CONFIG_SETTING_HEIGHTMAP_ROTATION_COUNTER_CLOCKWISE, STR_CONFIG_SETTING_HEIGHTMAP_ROTATION_CLOCKWISE, INVALID_STRING_ID};
-static const StringID _num_towns[]   = {STR_NUM_VERY_LOW, STR_NUM_LOW, STR_NUM_NORMAL, STR_NUM_HIGH, STR_NUM_CUSTOM, INVALID_STRING_ID};
-static const StringID _num_inds[]    = {STR_FUNDING_ONLY, STR_MINIMAL, STR_NUM_VERY_LOW, STR_NUM_LOW, STR_NUM_NORMAL, STR_NUM_HIGH, STR_NUM_CUSTOM, INVALID_STRING_ID};
-static const StringID _variety[]     = {STR_VARIETY_NONE, STR_VARIETY_VERY_LOW, STR_VARIETY_LOW, STR_VARIETY_MEDIUM, STR_VARIETY_HIGH, STR_VARIETY_VERY_HIGH, INVALID_STRING_ID};
+static const StringID _elevations[]  = {STR_TERRAIN_TYPE_VERY_FLAT, STR_TERRAIN_TYPE_FLAT, STR_TERRAIN_TYPE_HILLY, STR_TERRAIN_TYPE_MOUNTAINOUS, STR_TERRAIN_TYPE_ALPINIST, STR_TERRAIN_TYPE_CUSTOM};
+static const StringID _sea_lakes[]   = {STR_SEA_LEVEL_VERY_LOW, STR_SEA_LEVEL_LOW, STR_SEA_LEVEL_MEDIUM, STR_SEA_LEVEL_HIGH, STR_SEA_LEVEL_CUSTOM};
+static const StringID _rivers[]      = {STR_RIVERS_NONE, STR_RIVERS_FEW, STR_RIVERS_MODERATE, STR_RIVERS_LOT};
+static const StringID _smoothness[]  = {STR_CONFIG_SETTING_ROUGHNESS_OF_TERRAIN_VERY_SMOOTH, STR_CONFIG_SETTING_ROUGHNESS_OF_TERRAIN_SMOOTH, STR_CONFIG_SETTING_ROUGHNESS_OF_TERRAIN_ROUGH, STR_CONFIG_SETTING_ROUGHNESS_OF_TERRAIN_VERY_ROUGH};
+static const StringID _rotation[]    = {STR_CONFIG_SETTING_HEIGHTMAP_ROTATION_COUNTER_CLOCKWISE, STR_CONFIG_SETTING_HEIGHTMAP_ROTATION_CLOCKWISE};
+static const StringID _num_towns[]   = {STR_NUM_VERY_LOW, STR_NUM_LOW, STR_NUM_NORMAL, STR_NUM_HIGH, STR_NUM_CUSTOM};
+static const StringID _num_inds[]    = {STR_FUNDING_ONLY, STR_MINIMAL, STR_NUM_VERY_LOW, STR_NUM_LOW, STR_NUM_NORMAL, STR_NUM_HIGH, STR_NUM_CUSTOM};
+static const StringID _variety[]     = {STR_VARIETY_NONE, STR_VARIETY_VERY_LOW, STR_VARIETY_LOW, STR_VARIETY_MEDIUM, STR_VARIETY_HIGH, STR_VARIETY_VERY_HIGH};
 
-static_assert(lengthof(_num_inds) == ID_END + 1);
+static_assert(std::size(_num_inds) == ID_END);
 
 struct GenerateLandscapeWindow : public Window {
 	WidgetID widget_id;
diff --git a/src/gfx.cpp b/src/gfx.cpp
index 64bfc4a807..3d652ab18d 100644
--- a/src/gfx.cpp
+++ b/src/gfx.cpp
@@ -865,15 +865,15 @@ Dimension GetStringBoundingBox(StringID strid, FontSize start_fontsize)
 
 /**
  * Get maximum width of a list of strings.
- * @param list List of strings, terminated with INVALID_STRING_ID.
+ * @param list List of strings.
  * @param fontsize Font size to use.
  * @return Width of longest string within the list.
  */
 uint GetStringListWidth(std::span<const StringID> list, FontSize fontsize)
 {
 	uint width = 0;
-	for (const StringID *str = list.data(); *str != INVALID_STRING_ID; str++) {
-		width = std::max(width, GetStringBoundingBox(*str, fontsize).width);
+	for (auto str : list) {
+		width = std::max(width, GetStringBoundingBox(str, fontsize).width);
 	}
 	return width;
 }
@@ -887,8 +887,8 @@ uint GetStringListWidth(std::span<const StringID> list, FontSize fontsize)
 Dimension GetStringListBoundingBox(std::span<const StringID> list, FontSize fontsize)
 {
 	Dimension d{0, 0};
-	for (const StringID *str = list.data(); *str != INVALID_STRING_ID; str++) {
-		d = maxdim(d, GetStringBoundingBox(*str, fontsize));
+	for (auto str : list) {
+		d = maxdim(d, GetStringBoundingBox(str, fontsize));
 	}
 	return d;
 }
diff --git a/src/industry_gui.cpp b/src/industry_gui.cpp
index 863789f250..35cc27d837 100644
--- a/src/industry_gui.cpp
+++ b/src/industry_gui.cpp
@@ -1330,7 +1330,6 @@ protected:
 		STR_SORT_BY_TYPE,
 		STR_SORT_BY_PRODUCTION,
 		STR_SORT_BY_TRANSPORTED,
-		INVALID_STRING_ID
 	};
 	static const std::initializer_list<GUIIndustryList::SortFunction * const> sorter_funcs;
 
diff --git a/src/order_gui.cpp b/src/order_gui.cpp
index 06fb5318af..43101d1cd1 100644
--- a/src/order_gui.cpp
+++ b/src/order_gui.cpp
@@ -116,7 +116,6 @@ static const StringID _order_non_stop_drowdown[] = {
 	STR_ORDER_GO_NON_STOP_TO,
 	STR_ORDER_GO_VIA,
 	STR_ORDER_GO_NON_STOP_VIA,
-	INVALID_STRING_ID
 };
 
 static const StringID _order_full_load_drowdown[] = {
@@ -125,7 +124,6 @@ static const StringID _order_full_load_drowdown[] = {
 	STR_ORDER_DROP_FULL_LOAD_ALL,
 	STR_ORDER_DROP_FULL_LOAD_ANY,
 	STR_ORDER_DROP_NO_LOADING,
-	INVALID_STRING_ID
 };
 
 static const StringID _order_unload_drowdown[] = {
@@ -134,7 +132,6 @@ static const StringID _order_unload_drowdown[] = {
 	STR_ORDER_DROP_TRANSFER,
 	STR_EMPTY,
 	STR_ORDER_DROP_NO_UNLOADING,
-	INVALID_STRING_ID
 };
 
 static const StringID _order_goto_dropdown[] = {
@@ -142,7 +139,6 @@ static const StringID _order_goto_dropdown[] = {
 	STR_ORDER_GO_TO_NEAREST_DEPOT,
 	STR_ORDER_CONDITIONAL,
 	STR_ORDER_SHARE,
-	INVALID_STRING_ID
 };
 
 static const StringID _order_goto_dropdown_aircraft[] = {
@@ -150,7 +146,6 @@ static const StringID _order_goto_dropdown_aircraft[] = {
 	STR_ORDER_GO_TO_NEAREST_HANGAR,
 	STR_ORDER_CONDITIONAL,
 	STR_ORDER_SHARE,
-	INVALID_STRING_ID
 };
 
 /** Variables for conditional orders; this defines the order of appearance in the dropdown box */
@@ -174,7 +169,6 @@ static const StringID _order_conditional_condition[] = {
 	STR_ORDER_CONDITIONAL_COMPARATOR_MORE_EQUALS,
 	STR_ORDER_CONDITIONAL_COMPARATOR_IS_TRUE,
 	STR_ORDER_CONDITIONAL_COMPARATOR_IS_FALSE,
-	INVALID_STRING_ID,
 };
 
 extern uint ConvertSpeedToDisplaySpeed(uint speed, VehicleType type);
@@ -185,7 +179,6 @@ static const StringID _order_depot_action_dropdown[] = {
 	STR_ORDER_DROP_SERVICE_DEPOT,
 	STR_ORDER_DROP_HALT_DEPOT,
 	STR_ORDER_DROP_UNBUNCH,
-	INVALID_STRING_ID
 };
 
 static int DepotActionStringIndex(const Order *order)
@@ -204,7 +197,6 @@ static int DepotActionStringIndex(const Order *order)
 static const StringID _order_refit_action_dropdown[] = {
 	STR_ORDER_DROP_REFIT_AUTO,
 	STR_ORDER_DROP_REFIT_AUTO_ANY,
-	INVALID_STRING_ID
 };
 
 /**
diff --git a/src/station_gui.cpp b/src/station_gui.cpp
index d538fa33a2..c5de52e2e9 100644
--- a/src/station_gui.cpp
+++ b/src/station_gui.cpp
@@ -251,7 +251,6 @@ protected:
 		STR_SORT_BY_WAITING_AVAILABLE,
 		STR_SORT_BY_RATING_MAX,
 		STR_SORT_BY_RATING_MIN,
-		INVALID_STRING_ID
 	};
 	static const std::initializer_list<GUIStationList::SortFunction * const> sorter_funcs;
 
@@ -1291,7 +1290,6 @@ struct StationViewWindow : public Window {
 		STR_STATION_VIEW_WAITING_AMOUNT,
 		STR_STATION_VIEW_PLANNED_STATION,
 		STR_STATION_VIEW_PLANNED_AMOUNT,
-		INVALID_STRING_ID
 	};
 	/** Names of the grouping options in the dropdown. */
 	static inline const StringID group_names[] = {
@@ -1301,7 +1299,6 @@ struct StationViewWindow : public Window {
 		STR_STATION_VIEW_GROUP_V_D_S,
 		STR_STATION_VIEW_GROUP_D_S_V,
 		STR_STATION_VIEW_GROUP_D_V_S,
-		INVALID_STRING_ID
 	};
 
 	/**
diff --git a/src/town_gui.cpp b/src/town_gui.cpp
index e030111cdb..a4d9f40761 100644
--- a/src/town_gui.cpp
+++ b/src/town_gui.cpp
@@ -724,7 +724,6 @@ private:
 		STR_SORT_BY_NAME,
 		STR_SORT_BY_POPULATION,
 		STR_SORT_BY_RATING,
-		INVALID_STRING_ID
 	};
 	static const std::initializer_list<GUITownList::SortFunction * const> sorter_funcs;
 
diff --git a/src/vehicle_gui.cpp b/src/vehicle_gui.cpp
index 2b7e9c00ff..e4bcdb93fd 100644
--- a/src/vehicle_gui.cpp
+++ b/src/vehicle_gui.cpp
@@ -108,7 +108,6 @@ const std::initializer_list<const StringID> BaseVehicleListWindow::vehicle_group
 	STR_SORT_BY_LENGTH,
 	STR_SORT_BY_LIFE_TIME,
 	STR_SORT_BY_TIMETABLE_DELAY,
-	INVALID_STRING_ID
 };
 
 const std::initializer_list<const StringID> BaseVehicleListWindow::vehicle_group_none_sorter_names_wallclock = {
@@ -125,7 +124,6 @@ const std::initializer_list<const StringID> BaseVehicleListWindow::vehicle_group
 	STR_SORT_BY_LENGTH,
 	STR_SORT_BY_LIFE_TIME,
 	STR_SORT_BY_TIMETABLE_DELAY,
-	INVALID_STRING_ID
 };
 
 const std::initializer_list<BaseVehicleListWindow::VehicleGroupSortFunction * const> BaseVehicleListWindow::vehicle_group_shared_orders_sorter_funcs = {
@@ -142,7 +140,6 @@ const std::initializer_list<const StringID> BaseVehicleListWindow::vehicle_group
 	STR_SORT_BY_TOTAL_PROFIT_LAST_YEAR,
 	STR_SORT_BY_AVERAGE_PROFIT_THIS_YEAR,
 	STR_SORT_BY_AVERAGE_PROFIT_LAST_YEAR,
-	INVALID_STRING_ID
 };
 
 const std::initializer_list<const StringID> BaseVehicleListWindow::vehicle_group_shared_orders_sorter_names_wallclock = {
@@ -151,13 +148,11 @@ const std::initializer_list<const StringID> BaseVehicleListWindow::vehicle_group
 	STR_SORT_BY_TOTAL_PROFIT_LAST_PERIOD,
 	STR_SORT_BY_AVERAGE_PROFIT_THIS_PERIOD,
 	STR_SORT_BY_AVERAGE_PROFIT_LAST_PERIOD,
-	INVALID_STRING_ID
 };
 
 const std::initializer_list<const StringID> BaseVehicleListWindow::vehicle_group_by_names = {
 	STR_GROUP_BY_NONE,
 	STR_GROUP_BY_SHARED_ORDERS,
-	INVALID_STRING_ID
 };
 
 const StringID BaseVehicleListWindow::vehicle_depot_name[] = {
@@ -2362,14 +2357,12 @@ static StringID _service_interval_dropdown_calendar[] = {
 	STR_VEHICLE_DETAILS_DEFAULT,
 	STR_VEHICLE_DETAILS_DAYS,
 	STR_VEHICLE_DETAILS_PERCENT,
-	INVALID_STRING_ID,
 };
 
 static StringID _service_interval_dropdown_wallclock[] = {
 	STR_VEHICLE_DETAILS_DEFAULT,
 	STR_VEHICLE_DETAILS_MINUTES,
 	STR_VEHICLE_DETAILS_PERCENT,
-	INVALID_STRING_ID,
 };
 
 /** Class for managing the vehicle details window. */