OpenStreetMap
I like to map trees. Last year, I wrote a diary about trees mapping, a wiki page to document tagging of Italian monumental trees tagging, a trivia thread about the tallest trees in the database etc. In this diary, I’d like to focus on quality assurance (QA) checks we can perform on tree data. Many of these checks have been turned in MapRoulette challenges in my Tree Validation project.
Measures 📐
• Circumference
The circumference=* tag is used to describe the circumference of a tree’s trunk at a height of 1.3 metres above the ground, with the implied unit of measure being metres. Therefore, circumference=2.3 describes a trunk with a circumference of 2.3 metres.
According to the Guinness World Records, the greatest circumference for a tree is 43 metres. Trees with circumferences exceeding this value are likely errors. Often people forget that metres is the standard unit, so they tag using centimetres, creating giant trees. E.g. they tag circumference=650 instead of circumference=6.50.
• Height
The height=* tag is used to describe the height of a tree in metres. Therefore, height=15 describes a tree that is 15 metres tall.
Hyperion is a coast redwood (Sequoia sempervirens) in California that is the world’s tallest known living tree, measuring 115.92 m. Trees with height exceeding this value are likely errors.
• Specific species measures
You can refine the above checks using known limits for individual species. For example, according to monumentaltrees.com, the biggest circumference for a Tilia cordata is 12.81 (instead of 43) and the tallest specimen is 41.60 (instead of 115.92).
• The “slenderness ratio”
The height-to-circumference ratio can be considered a form of “slenderness ratio”: lower values indicate stocky or stout trees, while higher values indicate slender or spindly trees. This can be helpful to find wrong circumference or heights.