JOSM #101: Part II

Studies in Advanced OSM Alchemy

Draw basic building

Begin by drawing nodes to make a polygon, the last nodes needs to intersect the 1st node. Double-click to complete polygon. After you complete the polygon if you need to straighten out the lines you can use the shortcut ‘Q’.

In JOSM, use the Select tool (shortcut=S) to select objects. Be aware that you can select both nodes and edges. Often you just want to select a building or a highway by just clicking on the edge to modify the tags.

Draw with building tool

The building tools let you draw buildings with less clicks. It allows you to trace one side of a rectangular building, and then you can extend the shape. It also automatically applies the building=yes tag to the building.

How to Join Buildings

Often drawing complex buildings are easier by breaking it down into small pieces, then joining them.

Shift building polygon to base of building

Building polygons should be drawn to overlap the base of the building. There is a noticeable difference between the base of the building and the roof for tall buildings when imagery is taken at an oblique angle. A good strategy for drawing these buildings is to trace the top of the building first, then move the polygon towards the base of the building.

Draw points, water tower example

You can draw a point feature in JOSM by just selecting the Draw Nodes tool and double-clicking. You can then add the necessary tags, the correct tag for a water tower is man_made=water_tower

Note that some features such as water towers, pools, and basketball courts can be drawn with either a polygon or a point.

Draw basketball court

In this example a basketball court is drawn as a point with the following tags:

leisure=pitch sport=basketball

Draw pool

In this example a pool is drawn as a polygon with the following tag:


Validate your work

Validation can be run to detect errors in the map. Open the validation window and perform validation. It will return a list of warnings, you can go over these warnings and zoom in and select different types of errors and fix them.