PdfManual
From OpenStreetMap
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It is intended that the text below will form the basis of a manual in pdf form. The intended audience for the manual is the first time user of OSM, and as such as little prior knowledge of GPS is to be assumed. Each section below probably relating to one chapter.
Contents |
Introduction
This manual is intended as a brief introduction to the OpenStreetMap (OSM) project (http://www.openstreetmap.org/). Further, and more detailed, information can be found on the project's wiki (http://wiki.openstreetmap.org/), which is also likely to be more current.
Why is OSM neeeded?
The OSM project was started to enable people to use maps in creative, productive or unexpected ways. The use of traditional maps is hampered by legal and technical restrictions that severely curtail their use. The aim of the OSM project is to create free geographic data, like street maps, that can be used by anyone, anywhere.
Geographical data (geo data) is not free in many parts of the world, including the United Kingdom and much of Europe. Generally these places have given the task of mapping to various government agencies who in return get to make money by selling the data back to you and me. The USA is the only major counter-example where due to copyright restrictions on the government, they have to give it away free.
Collaborative mapping is an emerging and rapidly growing activity that has developed alongside other activities like geo-caching, that is being driven in part by technology such as cheap GPS (Global Positioning System) equipment, and online collaboration tools, like OpenStreetMap.org. What makes projects like this one stand out is their ethos on knowledge production and ownership. Under free software models the rights of authorship are de-centred and the ownership of knowledge is seen as a common resource that can be distributed and re-used without too much restrictions in the license. Opening up map making in this way has real potential to empower people to create their own knowledge and encourages re-use of cartographic resources in novel and creative ways.
How is the data gathered?
The position of roads, paths and other map features are recorded using widely available GPS units, which derive their location using satellite signals. Then, using software developed by the OSM project, this data is used to create the map infomation.
How to add data to OpenStreetMap
Summary
Essentially there are four stages to adding data to OSM.
- The actual position of roads, footpaths and other map features is recorded using a GPS (Global Positioning System) receiver, which can record tracks and points of interest.
- The tracks are then converted into a format suitable for OSM.
- The GPS tracks are uploaded to the OSM database where they form a permanent record of the fact that the map features were recorded personally by a contributor to the OSM project.
- Streets, paths and other feautes are »drawn« over the top of the GPS tracks using one of the editing tools available.
The current view of contributors to OSM is that proprietary material should not be used even at the stage of planning which areas to map or which routes you are going to take.
Recording GPS Tracks
A constellation of more than two dozen GPS satellites broadcasts precise timing signals by radio to GPS receivers, allowing them to accurately determine their location (longitude, latitude, and altitude) in any weather, day or night, anywhere on Earth.
A number of manufacturers produce dedicated GPS receivers, and a review of some models is posted on the OSM wiki. There are also GPS receivers designed to work with PDA devices and laptops.
Having obtained a GPS receiver you travel the route you wish to record. As you do so the GPS receiver records the track you are taking.
Formatting for OSM
OpenStreetMap uses GPS Exchange Format (http://www.topografix.com/gpx.asp) (GPX) files for uploading and publishing trackpoints. Most GPS units have their own data format which must be converted to GPX format. GPSBabel (http://www.gpsbabel.org/) can convert from a wide variety of formats into GPX.
If you have a Garmin and Magellan GPS unit you may skip this paragraph. Using the software supplied with your GPS unit download your tracklog to your computer and then convert it into GPX format.
GPSBabel directly supports Garmin and Magellan GPS units. You can connect your GPS via a serial cable to your computer, (if you lack a serial port you will need a serial to USB converter). You can then read the Garmin tracklog direct from the GPS unit and use GPSBabel to output a GPX fomat file suitable for OSM.
Uploading to OSM
Prior to uploading a file to OSM you need to create an account.
You can then upload your GPX file directly through the web site.
It is important to upload your GPX tracks, as this then forms a permanent record of the fact that the data was collected by your own efforts, and not copied from an existing map or other copyrighted source which is not licensed under CC-BY-SA 2.0 to you.
Editing
The editing of OSM data is covered in a subsequent chapter.
Editing
Introduction
It is crucially important when adding any data to the OSM project, such as names of streets etc, that all details have been personally recorded by yourself and that no details are taken from any source which is copyright and not licensed to you under CC-BY-SA 2.0.
Editing Conventions
Nodes
A physical road, street,footpath etc is initially drawn as a series of nodes which define points on a road or path etc. Nodes should be placed wherever there is a junction between two roads etc, or, where a road curves, a series of nodes should be placed so as the segments drawn between them create the curve. Nodes can also be placed where there is a particular point of interest (such as a hotel, car parking, church etc).
Segments
Nodes are joined together to form line segments, which define the path of the road or path, to produce the basic map. If a street is one way then, when drawing the segment, draw it in the direction of permitted travel. Currently to assist rendering (the production of printed maps from the OSM data) it is also helpful if all segments which will belong to a particular way are drawn in the same direction.
Ways
Segments are grouped together to form a »way«. In general a way would represent a specific road, or pathway, but in particular cases (such as motorways/intersate highways/autobahns) where a particular road might be very long, then it might be represented by a series of ways. A way can then be anotated with tags to describe what it represents, its name, and any other attribute of interest. Although there is no requirement to use standardised tags, there is benefit in editors of map content agreeing a core set of features together with corresponding keys and values in order that generic client software can interpret and display a common basemap, and some of these are listed in Appendix 1. A more complete list can be found on the wiki at http://wiki.openstreetmap.org/index.php/Map_Features
Specific Road Features
Dual Carriageways
A dual carriageway (or separated highway) should be drawn as two separate paths. The general rule is that if it is not possible to turn across the street at any junction then it should be drawn as two paths. If there are limited turning points then these should be explicitly marked as a link between the two carriageways. Nodes should be aligned in pairs along the two carriageways, so the line segments run in parallel. Each carriageway should be created as a separate way.
Roundabouts
A standard size roundabout with up to four exits can be drawn simply using four nodes in a diamond shape. A road can be connected to each of the nodes. A larger roundabout may benefit from using eight or even more nodes. Where a dual carriageway connects to a roundabout, there should be two nodes on the roundabout in place of just one.
The Editors
There are a number of alternatives available for marking nodes, drawing segments, and grouping segments to form ways.
Online Applet
(outdated text deleted, needs to be replaced with something similar to Potlatch/Primer)
JOSM
JOSM handles things very nicely, and with the appropriate plugin has a Landsat overlay. It will either read in GPX tracks from your hard disk, or if you have uploaded a GPS track to OSM it can then download them from OSM. If you are working on an area which already has OSM data on it you can download the OSM data as one layer, and have your GPS tracks from you hard drive as another layer, which stops you working on exactly the same track as already exists in OSM. Once you have drawn your line segments and made ways out of them you can then upload then to OSM.
You can easily, and quickly, zoom and scroll around a particular area, which makes editing the data particularly fast.
You can add a node in the middle of an existing segment.
