• Alysa Chen, Vassar College

A YouthMappers Introduction to Java OpenStreetMap (JOSM)

JOSM Logo. Square blue, yellow, red, and green map background with large brown pencil across map.

Welcome! My name is Alysa, and I’m a part of Hudson Valley Mappers, the YouthMappers chapter at Vassar College. I recently participated in the USAID GeoCenter + YouthMappers virtual internship for the spring 2021 semester and have a handful of practical information and advice to share about learning new geospatial tools! In this blog post, we’ll be

learning about JOSM- a free desktop editing tool for OpenStreetMap (OSM) that will make you a quicker and more efficient mapper.

Learning how to use new software can be intimidating. As a social-sciences-focused liberal arts college student, I was immediately alarmed by the complexity and technicality of introductory JOSM tutorials. In retrospect, however, I had subconsciously made it far more daunting than it actually was by treating it like a foreign language. In more simplistic terms, JOSM is an advanced OpenStreetMap editor with many handy shortcuts and plugins. Once you have learned a few shortcuts and plugins, editing will be much quicker and easier than iD. If you’re like me and have some beginner experience (or more) with using iD, you’ll recognize many of the same functions and tools in JOSM. Edits in JOSM also don’t have to be complex—you can map roads and buildings very efficiently for tasks on the Humanitarian OSM Team (HOT) Tasking Manager or in your own neighborhood. Despite the slightly intimidating interface, hurdling over the initial learning curve will earn you a more efficient—and enjoyable—editing workflow. Additionally, if you want to progress from being an OSM editor to validating edits on the HOT Tasking Manager, you are going to have to learn JOSM.

iD and JOSM: What are some similarities and differences?

The basic modes of operation of both editors are quite similar. Both iD and JOSM allow you to add, delete, edit features based on the OSM data model and add tags or attribute information to those geographic features. In iD, these are referred to as points, lines, and areas while in JOSM as nodes, ways, and relations. The iD terminology will be more familiar for those with a GIS background and JOSM for those more familiar with the OSM data model. Don’t let these terms confuse you: nodes are simply points in space, and ways are an ordered list of nodes. When a list of nodes share a start and end node, it forms an area.

One main difference is that JOSM is better suited for less stable internet or lower bandwidth when compared to iD. After downloading your preferred data, you will be able to edit offline on JOSM and then upload them later when you have stronger internet access again. Another important difference is that JOSM includes many more shortcuts and plugin tools that speed up the otherwise repetitive process of, for instance, redrawing all four corners of each building area or drawing buildings one at a time. The editor also offers stronger validation tools to ensure that your edits will be accepted.

Plugins are installable JOSM features that modify and extend basic editing features. For instance, the building tool plugin is a popular choice because it allows you to draw buildings twice as fast by only needing to click 2 or 3 times. To learn more about how this plugin works and more tips on drawing buildings, watch this video tutorial. For tips on mapping and editing roads on JOSM, watch this video tutorial. Helpful tools like splitting ways and combining nodes in a circle will be available through downloading the plugin utilsplugin2. The mapathoner plugin will allow you to draw, select, and square multiple objects at once. Some other shortcuts unique to JOSM are: exclude/extend areas, rotate and size up/down areas, and join overlapping areas. All of these shortucts help you edit buildings efficiently. A cheat sheet for the keyboard shortcuts can be found here and a shortcuts guide can be found here.

In addition to speeding up repetitive edits, both iD and JOSM share the abilities to switch between imagery (for iD, the “Background” tab, for JOSM, “Imagery”), tag elements with attributes/descriptions (such as road classification or building), and detect errors in editing (for iD, the “Issues” tab, for JOSM, the validation tool). Both allow you to correct for imagery offset, meaning to adjust the imagery layer to best match the mapped features. All of these perks help you map with more precision and accuracy.

JOSM Keyboard Shortcuts Cheat Sheet. Image of gray keyboard with shortcut keys colored. Table below keyboard explains shortcuts.

Tips for learning JOSM for the first time

Shake off the fear! First, get comfortable with your best friend, iD Editor. After you are fairly comfortable with using iD, challenge yourself to start editing with JOSM and you will grow as a YouthMappers member. Actively look for resources, tutorials, forums, and helpful links whether you are trying to figure out where to start (JOSM guide and video tutorial) or feel stuck because you can’t figure out how to do something (JOSM guide for troubleshooting).

From personal experience, learning along with other students and asking for help from those with more JOSM experience can help you along the way. Finding your own inspiration and reasons that draw you to mapping in the first place will also help make the process an enjoyable and rewarding experience. There are a myriad of ways in which JOSM can be applied to help you address the causes that you care about. Offline editing is a major bonus for field work and data collection, whether you are in the humanitarian, environmental, or educational sectors. In addition to being applied to humanitarian and social justice work, organizations, companies, or businesses can also use JOSM to fill in much-needed free and open source data for certain regions. Last but not least, you can build upon your personal skill set.

Don’t forget that everyone can be a mapper and contribute their effort to OSM. Have fun exploring JOSM and happy mapping!

About the Author:

Alysa Chen is a rising junior studying Geography at Vassar College, with a focus on human and political geography. She was born and raised in New York City. She is interested in the intersection of environmental, racial, and social justice. When she has free time, she enjoys volunteering locally, cooking, dancing, writing, and walking around her neighborhood.