diff --git a/roentgen/constructor.py b/roentgen/constructor.py
index 8ecf97f..5e3a85f 100644
--- a/roentgen/constructor.py
+++ b/roentgen/constructor.py
@@ -170,20 +170,20 @@ class Constructor:
         Construct Röntgen ways.
         """
         way_number: int = 0
-        for way_id in self.map_.way_map:  # type: int
+        for way_id in self.map_.ways:  # type: int
             ui.progress_bar(
                 way_number,
-                len(self.map_.way_map),
+                len(self.map_.ways),
                 step=10,
                 text="Constructing ways",
             )
             way_number += 1
-            way: OSMWay = self.map_.way_map[way_id]
+            way: OSMWay = self.map_.ways[way_id]
             if not self.check_level(way.tags):
                 continue
             self.construct_line(way, [], [way.nodes])
 
-        ui.progress_bar(-1, len(self.map_.way_map), text="Constructing ways")
+        ui.progress_bar(-1, len(self.map_.ways), text="Constructing ways")
 
     def construct_line(
         self,
@@ -294,8 +294,8 @@ class Constructor:
         """
         Construct Röntgen ways from OSM relations.
         """
-        for relation_id in self.map_.relation_map:
-            relation: OSMRelation = self.map_.relation_map[relation_id]
+        for relation_id in self.map_.relations:
+            relation: OSMRelation = self.map_.relations[relation_id]
             tags = relation.tags
             if not self.check_level(tags):
                 continue
@@ -306,11 +306,11 @@ class Constructor:
             for member in relation.members:  # type: OSMMember
                 if member.type_ == "way":
                     if member.role == "inner":
-                        if member.ref in self.map_.way_map:
-                            inner_ways.append(self.map_.way_map[member.ref])
+                        if member.ref in self.map_.ways:
+                            inner_ways.append(self.map_.ways[member.ref])
                     elif member.role == "outer":
-                        if member.ref in self.map_.way_map:
-                            outer_ways.append(self.map_.way_map[member.ref])
+                        if member.ref in self.map_.ways:
+                            outer_ways.append(self.map_.ways[member.ref])
                     else:
                         print(f'Unknown member role "{member.role}".')
             if outer_ways:
@@ -325,8 +325,8 @@ class Constructor:
         node_number: int = 0
 
         sorted_node_ids: Iterator[int] = sorted(
-            self.map_.node_map.keys(),
-            key=lambda x: -self.map_.node_map[x].coordinates[0],
+            self.map_.nodes.keys(),
+            key=lambda x: -self.map_.nodes[x].coordinates[0],
         )
 
         missing_tags = Counter()
@@ -334,9 +334,9 @@ class Constructor:
         for node_id in sorted_node_ids:  # type: int
             node_number += 1
             ui.progress_bar(
-                node_number, len(self.map_.node_map), text="Constructing nodes"
+                node_number, len(self.map_.nodes), text="Constructing nodes"
             )
-            node: OSMNode = self.map_.node_map[node_id]
+            node: OSMNode = self.map_.nodes[node_id]
             flung = self.flinger.fling(node.coordinates)
             tags = node.tags
 
@@ -379,4 +379,4 @@ class Constructor:
                 if key not in icon_set.processed
             )
 
-        ui.progress_bar(-1, len(self.map_.node_map), text="Constructing nodes")
+        ui.progress_bar(-1, len(self.map_.nodes), text="Constructing nodes")
diff --git a/roentgen/osm_reader.py b/roentgen/osm_reader.py
index 4b6c046..58356db 100644
--- a/roentgen/osm_reader.py
+++ b/roentgen/osm_reader.py
@@ -59,6 +59,9 @@ class OSMNode(Tagged):
 
     @classmethod
     def from_xml_structure(cls, element, is_full: bool = False) -> "OSMNode":
+        """
+        Parse node from OSM XML `<node>` element.
+        """
         node = cls()
         attributes = element.attrib
         node.id_ = int(attributes["id"])
@@ -114,6 +117,9 @@ class OSMWay(Tagged):
 
     @classmethod
     def from_xml_structure(cls, element, nodes, is_full: bool) -> "OSMWay":
+        """
+        Parse way from OSM XML `<way>` element.
+        """
         way = cls(int(element.attrib["id"]))
         if is_full:
             way.visible = element.attrib["visible"]
@@ -188,6 +194,9 @@ class OSMRelation(Tagged):
 
     @classmethod
     def from_xml_structure(cls, element, is_full: bool) -> "OSMRelation":
+        """
+        Parse relation from OSM XML `<relation>` element.
+        """
         attributes = element.attrib
         relation = cls(int(attributes["id"]))
         if is_full:
@@ -245,39 +254,39 @@ class Map:
     """
 
     def __init__(self):
-        self.node_map: Dict[int, OSMNode] = {}
-        self.way_map: Dict[int, OSMWay] = {}
-        self.relation_map: Dict[int, OSMRelation] = {}
+        self.nodes: Dict[int, OSMNode] = {}
+        self.ways: Dict[int, OSMWay] = {}
+        self.relations: Dict[int, OSMRelation] = {}
 
         self.authors: Set[str] = set()
         self.time: MinMax = MinMax()
         self.boundary_box: List[MinMax] = [MinMax(), MinMax()]
 
-    def add_node(self, node: OSMNode):
+    def add_node(self, node: OSMNode) -> None:
         """
         Add node and update map parameters.
         """
-        self.node_map[node.id_] = node
+        self.nodes[node.id_] = node
         if node.user:
             self.authors.add(node.user)
         self.time.update(node.timestamp)
         self.boundary_box[0].update(node.coordinates[0])
         self.boundary_box[1].update(node.coordinates[1])
 
-    def add_way(self, way: OSMWay):
+    def add_way(self, way: OSMWay) -> None:
         """
         Add way and update map parameters.
         """
-        self.way_map[way.id_] = way
+        self.ways[way.id_] = way
         if way.user:
             self.authors.add(way.user)
         self.time.update(way.timestamp)
 
-    def add_relation(self, relation: OSMRelation):
+    def add_relation(self, relation: OSMRelation) -> None:
         """
         Add relation and update map parameters.
         """
-        self.relation_map[relation.id_] = relation
+        self.relations[relation.id_] = relation
 
 
 class OverpassReader:
@@ -321,6 +330,8 @@ class OverpassReader:
 class OSMReader:
     """
     OpenStreetMap XML file parser.
+
+    See https://wiki.openstreetmap.org/wiki/OSM_XML
     """
 
     def __init__(
@@ -375,7 +386,7 @@ class OSMReader:
             if element.tag == "way" and self.parse_ways:
                 self.map_.add_way(
                     OSMWay.from_xml_structure(
-                        element, self.map_.node_map, self.is_full
+                        element, self.map_.nodes, self.is_full
                     )
                 )
             if element.tag == "relation" and self.parse_relations:
diff --git a/test/test_osm_reader.py b/test/test_osm_reader.py
index fa8a681..030500a 100644
--- a/test/test_osm_reader.py
+++ b/test/test_osm_reader.py
@@ -19,8 +19,8 @@ def test_node() -> None:
   <node id="42" lon="5" lat="10" />
 </osm>"""
     )
-    assert 42 in map_.node_map
-    node: OSMNode = map_.node_map[42]
+    assert 42 in map_.nodes
+    node: OSMNode = map_.nodes[42]
     assert node.id_ == 42
     assert np.allclose(node.coordinates, np.array([10, 5]))
 
@@ -38,8 +38,8 @@ def test_node_with_tag() -> None:
   </node>
 </osm>"""
     )
-    assert 42 in map_.node_map
-    node: OSMNode = map_.node_map[42]
+    assert 42 in map_.nodes
+    node: OSMNode = map_.nodes[42]
     assert node.id_ == 42
     assert np.allclose(node.coordinates, np.array([10, 5]))
     assert node.tags["key"] == "value"
@@ -56,8 +56,8 @@ def test_way() -> None:
   <way id="42" />
 </osm>"""
     )
-    assert 42 in map_.way_map
-    way: OSMWay = map_.way_map[42]
+    assert 42 in map_.ways
+    way: OSMWay = map_.ways[42]
     assert way.id_ == 42
 
 
@@ -76,7 +76,7 @@ def test_nodes() -> None:
   </way>
 </osm>"""
     )
-    way: OSMWay = map_.way_map[2]
+    way: OSMWay = map_.ways[2]
     assert len(way.nodes) == 1
     assert way.nodes[0].id_ == 1
     assert way.tags["key"] == "value"
@@ -100,8 +100,8 @@ def test_relation() -> None:
   </relation>
 </osm>"""
     )
-    assert 3 in map_.relation_map
-    relation: OSMRelation = map_.relation_map[3]
+    assert 3 in map_.relations
+    relation: OSMRelation = map_.relations[3]
     assert relation.id_ == 3
     assert relation.tags["key"] == "value"
     assert len(relation.members) == 1