diff --git a/cartographer/mapping/map_builder.cc b/cartographer/mapping/map_builder.cc
index bed8e22..1a679d0 100644
--- a/cartographer/mapping/map_builder.cc
+++ b/cartographer/mapping/map_builder.cc
@@ -170,19 +170,21 @@ void MapBuilder::SerializeState(io::ProtoStreamWriter* const writer) {
   }
   // Next we serialize all node data.
   {
-    const auto node_data = sparse_pose_graph_->GetTrajectoryNodes();
+    const auto trajectory_nodes = sparse_pose_graph_->GetTrajectoryNodes();
     for (int trajectory_id = 0;
-         trajectory_id != static_cast<int>(node_data.size()); ++trajectory_id) {
+         trajectory_id != static_cast<int>(trajectory_nodes.size());
+         ++trajectory_id) {
       for (int node_index = 0;
-           node_index != static_cast<int>(node_data[trajectory_id].size());
+           node_index !=
+           static_cast<int>(trajectory_nodes[trajectory_id].size());
            ++node_index) {
         proto::SerializedData proto;
-        auto* const node_data_proto = proto.mutable_node_data();
+        auto* const node_proto = proto.mutable_node();
         // TODO(whess): Handle trimmed data.
-        node_data_proto->mutable_node_id()->set_trajectory_id(trajectory_id);
-        node_data_proto->mutable_node_id()->set_node_index(node_index);
-        *node_data_proto->mutable_trajectory_node() =
-            ToProto(*node_data[trajectory_id][node_index].constant_data);
+        node_proto->mutable_node_id()->set_trajectory_id(trajectory_id);
+        node_proto->mutable_node_id()->set_node_index(node_index);
+        *node_proto->mutable_node_data() =
+            ToProto(*trajectory_nodes[trajectory_id][node_index].constant_data);
         // TODO(whess): Only enable optionally? Resulting pbstream files will be
         // a lot larger now.
         writer->WriteProto(proto);
diff --git a/cartographer/mapping/proto/serialization.proto b/cartographer/mapping/proto/serialization.proto
index 60b9015..33bc11d 100644
--- a/cartographer/mapping/proto/serialization.proto
+++ b/cartographer/mapping/proto/serialization.proto
@@ -18,7 +18,7 @@ package cartographer.mapping.proto;
 
 import "cartographer/mapping/proto/sparse_pose_graph.proto";
 import "cartographer/mapping/proto/submap.proto";
-import "cartographer/mapping/proto/trajectory_node.proto";
+import "cartographer/mapping/proto/trajectory_node_data.proto";
 
 message Submap {
   optional SubmapId submap_id = 1;
@@ -26,13 +26,13 @@ message Submap {
   optional Submap3D submap_3d = 3;
 }
 
-message NodeData {
+message Node {
   optional NodeId node_id = 1;
-  optional TrajectoryNode trajectory_node = 5;
+  optional TrajectoryNodeData node_data = 5;
 }
 
 message SerializedData {
   optional Submap submap = 1;
-  optional NodeData node_data = 2;
+  optional Node node = 2;
   // TODO(whess): Add IMU data, odometry.
 }
diff --git a/cartographer/mapping/proto/trajectory_node.proto b/cartographer/mapping/proto/trajectory_node_data.proto
similarity index 93%
rename from cartographer/mapping/proto/trajectory_node.proto
rename to cartographer/mapping/proto/trajectory_node_data.proto
index 2016b76..8cbc528 100644
--- a/cartographer/mapping/proto/trajectory_node.proto
+++ b/cartographer/mapping/proto/trajectory_node_data.proto
@@ -19,8 +19,8 @@ package cartographer.mapping.proto;
 import "cartographer/sensor/proto/sensor.proto";
 import "cartographer/transform/proto/transform.proto";
 
-// Serialized state of a mapping::TrajectoryNode.
-message TrajectoryNode {
+// Serialized state of a mapping::TrajectoryNode::Data.
+message TrajectoryNodeData {
   optional int64 timestamp = 1;
   optional transform.proto.Quaterniond gravity_alignment = 2;
   optional sensor.proto.CompressedPointCloud
diff --git a/cartographer/mapping/trajectory_node.cc b/cartographer/mapping/trajectory_node.cc
index 3d7947d..ad2325a 100644
--- a/cartographer/mapping/trajectory_node.cc
+++ b/cartographer/mapping/trajectory_node.cc
@@ -24,8 +24,8 @@
 namespace cartographer {
 namespace mapping {
 
-proto::TrajectoryNode ToProto(const TrajectoryNode::Data& constant_data) {
-  proto::TrajectoryNode proto;
+proto::TrajectoryNodeData ToProto(const TrajectoryNode::Data& constant_data) {
+  proto::TrajectoryNodeData proto;
   proto.set_timestamp(common::ToUniversal(constant_data.time));
   *proto.mutable_gravity_alignment() =
       transform::ToProto(constant_data.gravity_alignment);
@@ -47,7 +47,7 @@ proto::TrajectoryNode ToProto(const TrajectoryNode::Data& constant_data) {
   return proto;
 }
 
-TrajectoryNode::Data FromProto(const proto::TrajectoryNode& proto) {
+TrajectoryNode::Data FromProto(const proto::TrajectoryNodeData& proto) {
   Eigen::VectorXf rotational_scan_matcher_histogram(
       proto.rotational_scan_matcher_histogram_size());
   for (int i = 0; i != proto.rotational_scan_matcher_histogram_size(); ++i) {
diff --git a/cartographer/mapping/trajectory_node.h b/cartographer/mapping/trajectory_node.h
index c7a9279..95c659b 100644
--- a/cartographer/mapping/trajectory_node.h
+++ b/cartographer/mapping/trajectory_node.h
@@ -22,7 +22,7 @@
 
 #include "Eigen/Core"
 #include "cartographer/common/time.h"
-#include "cartographer/mapping/proto/trajectory_node.pb.h"
+#include "cartographer/mapping/proto/trajectory_node_data.pb.h"
 #include "cartographer/sensor/range_data.h"
 #include "cartographer/transform/rigid_transform.h"
 
@@ -57,8 +57,8 @@ struct TrajectoryNode {
   transform::Rigid3d pose;
 };
 
-proto::TrajectoryNode ToProto(const TrajectoryNode::Data& constant_data);
-TrajectoryNode::Data FromProto(const proto::TrajectoryNode& proto);
+proto::TrajectoryNodeData ToProto(const TrajectoryNode::Data& constant_data);
+TrajectoryNode::Data FromProto(const proto::TrajectoryNodeData& proto);
 
 }  // namespace mapping
 }  // namespace cartographer
diff --git a/cartographer/mapping/trajectory_node_test.cc b/cartographer/mapping/trajectory_node_test.cc
index e89a772..141e288 100644
--- a/cartographer/mapping/trajectory_node_test.cc
+++ b/cartographer/mapping/trajectory_node_test.cc
@@ -20,7 +20,7 @@
 
 #include "Eigen/Core"
 #include "cartographer/common/time.h"
-#include "cartographer/mapping/proto/trajectory_node.pb.h"
+#include "cartographer/mapping/proto/trajectory_node_data.pb.h"
 #include "gtest/gtest.h"
 
 namespace cartographer {
@@ -37,7 +37,7 @@ TEST(TrajectoryNodeTest, ToAndFromProto) {
       sensor::CompressedPointCloud({{-1.f, 2.f, 0.f}}).Decompress(),
       Eigen::VectorXf::Unit(20, 4),
   };
-  const proto::TrajectoryNode proto = ToProto(expected);
+  const proto::TrajectoryNodeData proto = ToProto(expected);
   const TrajectoryNode::Data actual = FromProto(proto);
   EXPECT_EQ(expected.time, actual.time);
   EXPECT_TRUE(actual.gravity_alignment.isApprox(expected.gravity_alignment));