02. The OpenStreetMap Project

The OpenStreetMap Project

In the next lessons, you will write a course project in C++ using real map data and A* search to find a path between two points, just as you might see in a desktop or mobile mapping application. The project you will will write will be using data from the OpenStreetMap project.

The OpenStreetMap project is an open source, collaborative endeavor to create free, user-generated maps of every part of the world. These maps are similar to the maps you might use in Google Maps or the Apple Maps app on your phone, but they are completely generated by individuals who volunteer to perform ground surveys of their local environment.

Example OpenStreetMap with plotted path

Example OpenStreetMap with plotted path

OpenStreetMap Data

OpenStreetMap data can come in several different formats. The data that is used for this project comes in the form of an OSM XML file (.osm file), and we have provided a sample from the OpenStreetMap Wiki below. Although you may not have worked with this type of data before, have a look at the data below and try to guess which element types from the next quiz are present in the data. We are confident you can figure this out by carefully studying the data!

Have a look at the element types in the XML map data below. Which of the following types do you see in the data?
SOLUTION:
  • node
  • way
  • relation

<?xml version="1.0" encoding="UTF-8"?>
<osm version="0.6" generator="CGImap 0.0.2">
 <bounds minlat="54.0889580" minlon="12.2487570" maxlat="54.0913900" maxlon="12.2524800"/>
 <node id="298884269" lat="54.0901746" lon="12.2482632" user="SvenHRO" uid="46882" visible="true" version="1" changeset="676636" timestamp="2008-09-21T21:37:45Z"/>
 <node id="261728686" lat="54.0906309" lon="12.2441924" user="PikoWinter" uid="36744" visible="true" version="1" changeset="323878" timestamp="2008-05-03T13:39:23Z"/>
 <node id="1831881213" version="1" changeset="12370172" lat="54.0900666" lon="12.2539381" user="lafkor" uid="75625" visible="true" timestamp="2012-07-20T09:43:19Z">
  <tag k="name" v="Neu Broderstorf"/>
  <tag k="traffic_sign" v="city_limit"/>
 </node>
 ...
 <node id="298884272" lat="54.0901447" lon="12.2516513" user="SvenHRO" uid="46882" visible="true" version="1" changeset="676636" timestamp="2008-09-21T21:37:45Z"/>
 <way id="26659127" user="Masch" uid="55988" visible="true" version="5" changeset="4142606" timestamp="2010-03-16T11:47:08Z">
  <nd ref="292403538"/>
  <nd ref="298884289"/>
  ...
  <nd ref="261728686"/>
  <tag k="highway" v="unclassified"/>
  <tag k="name" v="Pastower Straße"/>
 </way>
 <relation id="56688" user="kmvar" uid="56190" visible="true" version="28" changeset="6947637" timestamp="2011-01-12T14:23:49Z">
  <member type="node" ref="294942404" role=""/>
  ...
  <member type="node" ref="364933006" role=""/>
  <member type="way" ref="4579143" role=""/>
  ...
  <member type="node" ref="249673494" role=""/>
  <tag k="name" v="Küstenbus Linie 123"/>
  <tag k="network" v="VVW"/>
  <tag k="operator" v="Regionalverkehr Küste"/>
  <tag k="ref" v="123"/>
  <tag k="route" v="bus"/>
  <tag k="type" v="route"/>
 </relation>
 ...
</osm>

Data Types Overview

Excellent work in guessing the types present in the data above! If you look closely at the XML element types in the sample above, you should see the three element types which are important to the code you will be writing: Nodes, Ways, and Relations.

Node

A node is one of the most basic elements in the OpenStreetMap data model. Each node indicates a single point with an identifier id, latitude lat, and longitude lon. There are other XML attributes in a node element that won't be relevant to this project, such as the user id and the timestamp when the node was added to the data set. Additionally, a node can have several tags which provide additional information.

Way

A way is an ordered list of nodes that represents a feature in the map. This feature could be a road, or a boundary of a park, or some other feature in the map. Each way has at least one tag which denotes some information about the way, and each way also belongs to at least one relation, which is described below.

Relation

A relation is a data structure which documents a relationship between other data elements. Examples from the OpenStreetMap wiki include:

  • A route relation which lists the ways that form a major highway, cycle route, or bus route.
  • A multipolygon that describes an area with holes, where the outer and inner boundaries of the area are given by two ways.

Example

To tie all of these three types together, consider the following example of mapping a large river with distinct banks on either side of the river.

Up Next

For your project, you will primarily be working with Nodes, although the code that we provide determines which nodes are connected as neighbors by using the ways and relations to which they belong. The code to parse this data and the data structures to store the data in your program have already been written in the IO2D OpenStreetMap example. In your project, you won't need to recreate any of this code - you will be writing code that extends this example to plot a path. Up next, you will learn how to build, run, and test your project code, and then we'll have an in-depth look at the starter code so you will be prepared to do the project.

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