Natural features changing advice?

[Minh_Nguyen]

@DunkeldHistory1

Well yesterday I was presenting to 9 year olds about what we can learn from historical maps and the changes in the river - the appearance of islands - really caught their imagination.

Hooray! Way to inspire the next generation!

@DunkeldHistory1

So, are there any mapped examples of watercourse changes in OHM? Do they work in time sequence?

Yes, there were some examples in the following thread:

Mapping waterway changes - adding/losing land

I am mapping a river and its changes (there will be a later followup topic on the best practice for mapping a much larger area of this river and its harbour once I understand the options here). The following 2 images show an aerial view of the river in 1944 and the OHM map for the current river profile/shoreline, which currently has no start_date. I can easily show in OHM the addition of land with time by adding a river area with no start-date and an end_date somewhere between 1944 and now. Th…

Here are a couple of admittedly trivial examples of former courses that I’ve mapped so far:

• Way: ‪Little Miami River‬ (‪198841228‬) | OpenHistoricalMap (follow the link to the chronology relation)
• Way: ‪Guadalupe River‬ (‪199813878‬) | OpenHistoricalMap
• Way: ‪North Fork Pacheco Creek‬ (‪199558479‬) | OpenHistoricalMap (didn’t “end”, just got inundated by a reservoir)

@DunkeldHistory1

My guess is the sequence does not consider tagged areas that have no start_date but do have an end_date?

Or is it that natural tags are not considered to change by the time sequencer?

The time slider doesn’t distinguish features by type. If something lacks a start_date=* tag, it’s assumed to have been around since the beginning of time. If it lacks an end_date=* tag, it’s assumed to exist in the present day. Most natural features in the database lack start and end dates, so we assume they’re extant features that have always been around in the current form. There’s certainly room for improvement.

A couple months ago, we added a validator rule to iD to remind mappers to add start dates to artificial features. However, we’ve exempted natural features because their dates are much more difficult to estimate; we didn’t want to shower mappers with these warnings, because they’d probably tune out the ones that matter. If you are able to determine dates on a waterway or other natural feature, please do tag it on the feature.