diff --git a/src/file.rs b/src/file.rs
index 6f22cf9..d1fd674 100644
--- a/src/file.rs
+++ b/src/file.rs
@@ -51,19 +51,19 @@ pub(crate) enum FourCC{
 }
 #[binrw]
 #[brw(little)]
-struct Header{
+pub struct Header{
 	/// Type of file
-	fourcc:FourCC,
-	/// Type version
-	version:u32,
+	pub fourcc:FourCC,
+	/// File format version
+	pub version:u32,
 	/// Minimum data required to know the location of all streamable resources for this specific file
-	priming:u64,
+	pub priming:u64,
 	/// uuid for this file
-	resource:u128,
+	pub resource:u128,
 	//don't need try_calc: the struct will force field initialization anyways and it can be calculated there
-	block_count:u32,
+	pub block_count:u32,
 	#[br(count=block_count+1)]
-	block_location:Vec<u64>,
+	pub block_location:Vec<u64>,
 }
 
 #[binrw]
diff --git a/src/map.rs b/src/map.rs
index 8b2d91d..12fd577 100644
--- a/src/map.rs
+++ b/src/map.rs
@@ -284,6 +284,7 @@ impl<R:BinReaderExt> StreamableMap<R>{
 
 const BVH_NODE_MAX_WEIGHT:usize=64*1024;//64 kB
 fn collect_spacial_blocks(
+	block_location:&mut Vec<u64>,
 	block_headers:&mut Vec<SpacialBlockHeader>,
 	sequential_block_data:&mut std::io::Cursor<&mut Vec<u8>>,
 	bvh_node:strafesnet_common::bvh::BvhWeightNode<usize,newtypes::model::Model>
@@ -309,11 +310,12 @@ fn collect_spacial_blocks(
 			models,
 		};
 		binrw::BinWrite::write_le(&region,sequential_block_data).map_err(Error::InvalidData)?;
+		block_location.push(sequential_block_data.position());
 	}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,sequential_block_data,bvh_node)?;
+					collect_spacial_blocks(block_location,block_headers,sequential_block_data,bvh_node)?;
 				}
 			},
 			strafesnet_common::bvh::RecursiveContent::Leaf(_)=>panic!(),//bvh branches are 20 leaves minimum
@@ -337,33 +339,36 @@ pub fn write_map<W:BinWriterExt>(mut writer:W,map:strafesnet_common::map::Comple
 	}).collect::<Result<Vec<_>,_>>()?;
 	let bvh=strafesnet_common::bvh::generate_bvh(boxen).weigh_contents(&|_|std::mem::size_of::<newtypes::model::Model>());
 	//build blocks
-	let mut spacial_blocks=Vec::new();//for header
+	let mut block_location=vec![0];//for file header
+	let mut spacial_blocks=Vec::new();//for map header
 	let mut sequential_block_data=Vec::new();
 	let mut cursor_to_data=std::io::Cursor::new(&mut sequential_block_data);
-	collect_spacial_blocks(&mut spacial_blocks,&mut cursor_to_data,bvh)?;
-	let mut block_id=spacial_blocks.len() as u32;//continue block id
-	let mut resource_blocks=Vec::new();//for header
+	collect_spacial_blocks(&mut block_location,&mut spacial_blocks,&mut cursor_to_data,bvh)?;
+	let mut block_count=spacial_blocks.len() as u32;//continue block id
+	let mut resource_blocks=Vec::new();//for map header
 	//meshes
 	for mesh in map.meshes.into_iter(){
 		resource_blocks.push(ResourceBlockHeader{
 			resource:ResourceType::Mesh,
-			id:BlockId::new(block_id),
+			id:BlockId::new(block_count),
 		});
-		block_id+=1;
+		block_count+=1;
 		let serializable_mesh:newtypes::model::Mesh=mesh.into();
 		binrw::BinWrite::write_le(&serializable_mesh,&mut cursor_to_data).map_err(Error::InvalidData)?;
+		block_location.push(cursor_to_data.position());
 	}
 	//textures
 	for mut texture in map.textures.into_iter(){
 		resource_blocks.push(ResourceBlockHeader{
 			resource:ResourceType::Texture,
-			id:BlockId::new(block_id),
+			id:BlockId::new(block_count),
 		});
-		block_id+=1;
+		block_count+=1;
 		sequential_block_data.append(&mut texture);
+		block_location.push(sequential_block_data.len() as u64);
 	}
 	//build header
-	let header=MapHeader{
+	let map_header=MapHeader{
 		num_spacial_blocks:spacial_blocks.len() as u32,
 		num_resource_blocks:resource_blocks.len() as u32,
 		num_resources_external:0,
@@ -377,8 +382,31 @@ pub fn write_map<W:BinWriterExt>(mut writer:W,map:strafesnet_common::map::Comple
 		attributes:map.attributes.into_iter().map(Into::into).collect(),
 		render_configs:map.render_configs.into_iter().map(Into::into).collect(),
 	};
-	//write header
-	writer.write_le(&header).map_err(Error::InvalidData)?;
+	let mut file_header=crate::file::Header{
+		fourcc:crate::file::FourCC::Map,
+		version:0,
+		priming:0,//TODO
+		resource:0,
+		block_count,
+		block_location,
+	};
+	//probe header lengths
+	let mut file_header_data=Vec::new();
+	binrw::BinWrite::write_le(&file_header,&mut std::io::Cursor::new(&mut file_header_data)).map_err(Error::InvalidData)?;
+	let mut map_header_data=Vec::new();
+	binrw::BinWrite::write_le(&map_header,&mut std::io::Cursor::new(&mut map_header_data)).map_err(Error::InvalidData)?;
+
+	//update file header according to probe data
+	let offset=file_header_data.len() as u64+map_header_data.len() as u64;
+	file_header.priming=offset;
+	for position in &mut file_header.block_location{
+		*position+=offset;
+	}
+
+	//write file header
+	writer.write_le(&file_header).map_err(Error::InvalidData)?;
+	//write map header
+	writer.write(&map_header_data).map_err(Error::IO)?;
 	//write blocks
 	writer.write(&sequential_block_data).map_err(Error::IO)?;
 	Ok(())