diff --git a/nav2_amcl/include/nav2_amcl/amcl_node.hpp b/nav2_amcl/include/nav2_amcl/amcl_node.hpp
index 030a85f38cd..950c839796b 100644
--- a/nav2_amcl/include/nav2_amcl/amcl_node.hpp
+++ b/nav2_amcl/include/nav2_amcl/amcl_node.hpp
@@ -152,7 +152,8 @@ class AmclNode : public nav2_util::LifecycleNode
   std::recursive_mutex mutex_;
   rclcpp::Subscription<nav_msgs::msg::OccupancyGrid>::ConstSharedPtr map_sub_;
 #if NEW_UNIFORM_SAMPLING
-  static std::vector<std::pair<int, int>> free_space_indices;
+  struct Point2D { int32_t x; int32_t y; };
+  static std::vector<Point2D> free_space_indices;
 #endif
 
   // Transforms
diff --git a/nav2_amcl/include/nav2_amcl/map/map.hpp b/nav2_amcl/include/nav2_amcl/map/map.hpp
index c9557efa0b0..3cf6f0d597b 100644
--- a/nav2_amcl/include/nav2_amcl/map/map.hpp
+++ b/nav2_amcl/include/nav2_amcl/map/map.hpp
@@ -41,20 +41,21 @@ struct _rtk_fig_t;
 // Limits
 #define MAP_WIFI_MAX_LEVELS 8
 
-
+// make sure that the sizeof(map_cell_t) == 5
+#pragma pack(push, 1)
 // Description for a single map cell.
 typedef struct
 {
   // Occupancy state (-1 = free, 0 = unknown, +1 = occ)
-  int occ_state;
+  int8_t occ_state;
 
   // Distance to the nearest occupied cell
-  double occ_dist;
+  float occ_dist;
 
   // Wifi levels
   // int wifi_levels[MAP_WIFI_MAX_LEVELS];
 } map_cell_t;
-
+#pragma pack(pop)
 
 // Description for a map
 typedef struct
diff --git a/nav2_amcl/src/amcl_node.cpp b/nav2_amcl/src/amcl_node.cpp
index cdd4c5adbdb..e68625d23b3 100644
--- a/nav2_amcl/src/amcl_node.cpp
+++ b/nav2_amcl/src/amcl_node.cpp
@@ -227,6 +227,11 @@ AmclNode::AmclNode(const rclcpp::NodeOptions & options)
   add_parameter(
     "first_map_only", rclcpp::ParameterValue(false),
     "Set this to true, when you want to load a new map published from the map_server");
+
+  add_parameter(
+    "freespace_downsampling", rclcpp::ParameterValue(
+      false),
+    "If true, downsample the free space used by the Pose Generator. This will save memory in VERY large maps");
 }
 
 AmclNode::~AmclNode()
@@ -404,7 +409,7 @@ AmclNode::checkElapsedTime(std::chrono::seconds check_interval, rclcpp::Time las
 }
 
 #if NEW_UNIFORM_SAMPLING
-std::vector<std::pair<int, int>> AmclNode::free_space_indices;
+std::vector<AmclNode::Point2D> AmclNode::free_space_indices;
 #endif
 
 bool
@@ -446,10 +451,10 @@ AmclNode::uniformPoseGenerator(void * arg)
 
 #if NEW_UNIFORM_SAMPLING
   unsigned int rand_index = drand48() * free_space_indices.size();
-  std::pair<int, int> free_point = free_space_indices[rand_index];
+  AmclNode::Point2D free_point = free_space_indices[rand_index];
   pf_vector_t p;
-  p.v[0] = MAP_WXGX(map, free_point.first);
-  p.v[1] = MAP_WYGY(map, free_point.second);
+  p.v[0] = MAP_WXGX(map, free_point.x);
+  p.v[1] = MAP_WYGY(map, free_point.y);
   p.v[2] = drand48() * 2 * M_PI - M_PI;
 #else
   double min_x, max_x, min_y, max_y;
@@ -1106,6 +1111,7 @@ AmclNode::initParameters()
   get_parameter("always_reset_initial_pose", always_reset_initial_pose_);
   get_parameter("scan_topic", scan_topic_);
   get_parameter("map_topic", map_topic_);
+  get_parameter("freespace_downsampling", freespace_downsampling_);
 
   save_pose_period_ = tf2::durationFromSec(1.0 / save_pose_rate);
   transform_tolerance_ = tf2::durationFromSec(tmp_tol);
@@ -1435,12 +1441,14 @@ AmclNode::handleMapMessage(const nav_msgs::msg::OccupancyGrid & msg)
 void
 AmclNode::createFreeSpaceVector()
 {
+  int delta = freespace_downsampling_ ? 2 : 1;
   // Index of free space
   free_space_indices.resize(0);
-  for (int i = 0; i < map_->size_x; i++) {
-    for (int j = 0; j < map_->size_y; j++) {
+  for (int i = 0; i < map_->size_x; i += delta) {
+    for (int j = 0; j < map_->size_y; j += delta) {
       if (map_->cells[MAP_INDEX(map_, i, j)].occ_state == -1) {
-        free_space_indices.push_back(std::make_pair(i, j));
+        AmclNode::Point2D point = {i, j};
+        free_space_indices.push_back(point);
       }
     }
   }