diff --git a/src/map.rs b/src/map.rs
index 5a97e8d..2df530f 100644
--- a/src/map.rs
+++ b/src/map.rs
@@ -135,15 +135,12 @@ struct ResourceExternalHeader{
 #[binrw]
 #[brw(little)]
 struct MapHeader{
-	num_nodes:u32,
 	num_spacial_blocks:u32,
 	num_resource_blocks:u32,
 	num_resources_external:u32,
 	num_modes:u32,
 	num_attributes:u32,
 	num_render_configs:u32,
-	#[br(count=num_nodes)]
-	nodes:Vec<u32>,
 	#[br(count=num_spacial_blocks)]
 	spacial_blocks:Vec<SpacialBlockHeader>,
 	#[br(count=num_resource_blocks)]
@@ -244,7 +241,7 @@ impl<R:BinReaderExt> StreamableMap<R>{
 	}
 	pub fn get_intersecting_region_block_ids(&self,aabb:&Aabb)->Vec<BlockId>{
 		let mut block_ids=Vec::new();
-		self.bvh.the_tester(aabb,&mut |block_id|block_ids.push(block_id));
+		self.bvh.the_tester(aabb,&mut |&block_id|block_ids.push(block_id));
 		block_ids
 	}
 	pub fn load_region(&mut self,block_id:BlockId)->Result<Vec<model::Model>,Error>{
@@ -285,11 +282,75 @@ impl<R:BinReaderExt> StreamableMap<R>{
 	}
 }
 
+const BVH_NODE_MAX_WEIGHT:usize=64*1024;//64 kB
+fn collect_spacial_blocks(block_headers:&mut Vec<SpacialBlockHeader>,block_datas:&mut Vec<Vec<u8>>,bvh_node:strafesnet_common::bvh::BvhWeightNode<usize,Vec<u8>>){
+	//inspect the node weights top-down.
+	//When a node weighs less than the limit,
+	//serialize its entire contents into a region block
+	if *bvh_node.weight()<BVH_NODE_MAX_WEIGHT{
+		let mut data=Vec::new();
+		let mut count=0;
+		let extents=bvh_node.aabb().clone().into();
+		bvh_node.into_visitor(&mut |mut model_data|{
+			count+=1;
+			data.append(&mut model_data);
+		});
+		let id=BlockId::new(block_headers.len() as u32);
+		block_headers.push(SpacialBlockHeader{
+			id,
+			extents,
+		});
+		block_datas.push(data);
+	}else{
+		match bvh_node.into_content(){
+			strafesnet_common::bvh::RecursiveContent::Branch(bvh_node_list)=>{
+				for bvh_node in bvh_node_list{
+					collect_spacial_blocks(block_headers,block_datas,bvh_node);
+				}
+			},
+			strafesnet_common::bvh::RecursiveContent::Leaf(_)=>panic!(),//bvh branches are 20 leaves minimum
+		}
+	}
+}
+
 /// TODO: Optionally provide a bot that describes the path through the map
 /// otherwise sort by distance to start zone
 pub fn write_map<W:BinWriterExt>(mut writer:W,map:strafesnet_common::map::CompleteMap)->Result<(),Error>{
+	//serialize models and make a bvh that knows the file size of the branch
+	let boxen=map.models.into_iter().map(|model|{
+		//grow your own aabb
+		let mesh=map.meshes.get(model.mesh.get() as usize).ok_or(Error::InvalidMeshId(model.mesh))?;
+		let mut aabb=strafesnet_common::aabb::Aabb::default();
+		for &pos in &mesh.unique_pos{
+			aabb.grow(model.transform.transform_point3(pos));
+		}
+		let serializable_model:newtypes::model::Model=model.into();
+		let mut data=Vec::new();
+		binrw::BinWrite::write_le(&serializable_model,&mut std::io::Cursor::new(&mut data)).map_err(Error::InvalidData)?;
+		Ok((data,aabb))
+	}).collect::<Result<Vec<_>,_>>()?;
+	let bvh=strafesnet_common::bvh::generate_bvh(boxen).weigh_contents(&|model|model.len());
 	//build blocks
+	let mut spacial_blocks=Vec::new();
+	let mut spacial_blocks_data=Vec::new();
+	collect_spacial_blocks(&mut spacial_blocks,&mut spacial_blocks_data,bvh);
+	let resource_blocks=Vec::new();
+	//let resource_blocks_data=Vec::new();
 	//build header
+	let header=MapHeader{
+		num_spacial_blocks:spacial_blocks.len() as u32,
+		num_resource_blocks:resource_blocks.len() as u32,
+		num_resources_external:0,
+		num_modes:map.modes.modes.len() as u32,
+		num_attributes:map.attributes.len() as u32,
+		num_render_configs:map.render_configs.len() as u32,
+		spacial_blocks,
+		resource_blocks,
+		external_resources:Vec::new(),
+		modes:map.modes.modes.into_iter().map(Into::into).collect(),
+		attributes:map.attributes.into_iter().map(Into::into).collect(),
+		render_configs:map.render_configs.into_iter().map(Into::into).collect(),
+	};
 	//write header
 	//write blocks
 	Ok(())