diff --git a/README.md b/README.md
index 2c24c09..614606f 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,11 @@
 # gpx-web-utils
 
 ![ci](https://github.com/thermokarst/gpx-web-utils/workflows/ci/badge.svg)
+
+## quickstart
+
+1. install [wasm-pack](https://rustwasm.github.io/wasm-pack/installer/)
+2. `wasm-pack build`
+3. `cd www`
+4. `npm install`
+5. `npm run start`
diff --git a/src/utils.rs b/src/utils.rs
index c8cd025..79e912a 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -9,16 +9,25 @@ pub fn translate_js_to_rust(files: js_sys::Array) -> Vec<String> {
 }
 
 pub fn join_gpx_files(files: Vec<String>) -> gpx::Gpx {
-    let mut merged: gpx::Gpx = Default::default();
+    let mut merged_gpx: gpx::Gpx = Default::default();
+    let mut merged_track: gpx::Track = gpx::Track::new();
 
     for file in files.iter() {
         let buffer = std::io::BufReader::new(file.as_bytes());
         let mut parsed_gpx: gpx::Gpx = gpx::read(buffer).expect("invalid gpx");
 
-        merged.tracks.append(&mut parsed_gpx.tracks);
-        merged.waypoints.append(&mut parsed_gpx.waypoints);
+        // consolidate all track segements into one single track.
+        for track in parsed_gpx.tracks {
+            for segment in track.segments {
+                merged_track.segments.push(segment);
+            }
+        }
+
+        merged_gpx.waypoints.append(&mut parsed_gpx.waypoints);
     }
 
+    merged_gpx.tracks.push(merged_track);
+
     let link = gpx::Link {
         href: String::from("https://gpx.thermokar.st"),
         ..Default::default()
@@ -32,10 +41,10 @@ pub fn join_gpx_files(files: Vec<String>) -> gpx::Gpx {
         author: Some(author),
         ..Default::default()
     };
-    merged.metadata = Some(metadata);
-    merged.version = gpx::GpxVersion::Gpx11;
+    merged_gpx.metadata = Some(metadata);
+    merged_gpx.version = gpx::GpxVersion::Gpx11;
 
-    merged
+    merged_gpx
 }
 
 pub fn write_gpx_to_buffer(gpx: gpx::Gpx) -> Vec<u8> {