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Posted by on Oct 5, 2016 in GIS, Mapping, What's new | 0 comments

Tutorial: Digitisation in OpenStreetMap using JOSM : First Steps

Tutorial: Digitisation in OpenStreetMap using JOSM : First Steps

This tutorial is designed to teach you how to quickly and simply provide information to improve OpenStreetMap (OSM) using the Java OpenStreetMap Editor (JOSM). It uses an example task of digitisation from the Tasking Manager of the Humanitarian OSM Team, specifically for the case of a humanitarian emergency. The tutorial is not designed to be exhaustive but rather to give you the information strictly necessary to begin. You will find more detailed information at the official website, LearnOSM.org. See the page “Remote Editing” (not yet translated from French).

The following is only an initial version, so please feel free to contact us if you wish to help us improve it (e.g. screen shots, editorial suggestions).

This post was originally written in French.

Getting Started

  1. (If you do not already have one) create an account at OpenStreetMap: https://www.openstreetmap.org/user/new
  2. Once you have logged in, you can begin to digitise OSM directly, using your Web browser (by clicking on « Modify » or « Modify with Potlach or ID »). However, using software specifically designed for OSM editing will facilitate your work considerably. We recommend that you download and install JOSM from:  https://josm.openstreetmap.de/wiki/Fr%3AWikiStart
  3. Start JOSM. Then go to “Edit/Preferences”. Click the “remote control” icon and check the box “Enable remote control”.
    Figure 1

    Figure 1

    Figure 1

  4. Now, go to the task you wish to work on (in our example, http://tasks.hotosm.org/project/585). The map you will see is divided into zones. Yellow zones are those already completed while green zones have, additionally, been validated by more experienced mappers. The clear zones are those which you can choose to work on yourself. Select one by clicking on it. Then lock this zone for two hours by clicking on “Start mapping”. During this two-hour period, no one else will be able to edit this zone through the tasking manager.
    fig2

    Figure 2
  5. On the following screen, select “JOSM” from the “Edit with” selection drop-down menu. The data needed for your session should then automatically load into JOSM.
    fig3

    Figure 3 
  6. In cases where mapping is urgently needed, a satellite or drone aerial image is often available. The source of the image (TMS link) will normally be indicated in the task Description in the tasking manager (e.g.,  http://wms.openstreetmap.fr/tms/1.0.0/haiti_2014/{zoom}/{x}/{y}).  To load the image into JOSM, follow “Edit/Preferences ==> WMS TMS” (see Figure  1) and click “+WMS” or “+TMS”, as appropriate for the source indicated. In the window form which opens, paste the address of the source and provide it with a name in the corresponding area. Click “Ok” to finish.
  7. Now, when you return to the JOSM main window, you can go to the “Imagery” menu and click to load, as a new layer, the image you just added. (Note that if no specific aerial image is available, you can use standard Bing images.)

Digitising

Digitisation itself is rather intuitive. The map layers are shown on the right. There is an “eye” icon that allows you to make layers visible / invisible. Use the arrow symbols to move the map layers up or down in the list.
You can also use keyboard/mouse shortcuts for the following basic tasks:

  • Hold the right mouse button down to drag the map.
  • Typing S activates the selection tool for a node, line segment or polygon.
  • The A key will enable you to add a node.
    (TIP: if you click the last node on a line after using A, you can further extend the line.)

Attributes can be assigned to map objects by opening the “Tag” box on the right of the screen whenever a node, line or polygon selection is active. You can add the attributes in one of two ways: manually (with Alt+A) if you already know them, or by searching the “Attributes” menu and choosing from the list of valid classifications (“presets”) for the type of object you have selected. For manual entry, it is likely that you will quickly learn the most common attribute classifications (e.g., “highway=residential”, “building=yes”). You can find a complete list of attributes for all observable objects at: http://wiki.openstreetmap.org/wiki/FR:Howto_Map_A

If you wish to learn more about OSM object attribute descriptions, please consult the following Wiki pages:

A variety of tools are useful for making your cartographic work more accurate and efficient. In the “Tools” menu, we suggest you examine how to use them. Most have keyboard shortcuts. Among these:

  • P: cut a line (e.g. a route) by inserting a node. Or use C to remove a node and merge the lines
  • After selecting a node, use M to merge it with another (existing) node
  • Q will render an object (e.g., a building) quadrilateral (90° angles). Shift-O will make it circular (e.g. a traffic circle)
  • L will align nodes to a straight line (e.g., to create a straight route)

Tip : when you map a new waterway, road, etc. which continues beyond the zone you are working on, add a node just slightly outside your zone (i.e., in the contiguous hashed area). By doing so, the person who next works on that adjacent area will be able to use your node and easily continue the feature.

Send your data to the OSM server

Once you have finished your chosen zone, you can send the data to the OSM server. To do so, select “File ==>Upload data”.

You will see an area in the OSM Task Manager reserved for commenting on the work you have done. You can add what you like (e.g., “added buildings and a residential road”) but always be sure that the default comment text, as shown in the “Instructions” tab of the Task Manager, precedes any additional text you provide.

  • Sometimes, alerts are present for the zone you are working on. If so, a toolbox and a checkbox will be present on the lower right of the JOSM screen so that you can resolve any issues shown. Issues are grouped by category. If you double-click on one of them, the mapped object(s) affected by the alert will be shown in red (to help you easily locate them).
  • A data conflict can sometimes occur between your data and data held on the server (e.g., multiple modifications are pending). In such cases, you should ask for help from an experienced OSM cartographer.

Once you have finished your work session, on the Tasking Manager screen don’t forget to click either “Mark task as done” (if you have completed all work on the zone) or “Stop mapping” (if, for example, you want to take a break but there is still more work to do on that zone).

Thank you for your contribution ! Users of the map, be they humanitarian teams or local communities, greatly appreciate your efforts.

Tutorial created by: Pierre Loicq, Léo Martine, Martin Noblecourt
(EN translation: Robert Danziger)

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This article have been written collectively by CartONG's team, check the bottom of the text for the list of authors!