[talk-ph] On editing PH coastlines

[Mike Collinson]

Easter greetings to all.

Here are my personal rules of thumb for mapping from Landsat, other views most welcome, these are just my opinions:

- Most of the people looking at our maps will do so from land. They want to orientate the map with what they see.  It they see something on a map but not in reality, it is easy to conclude that it is high tide.  But if it is not on the map but there in reality, then the map looks wrong. Moral: If in doubt, map as land.

- It is not possible to know whether a landsat image was made at high tide or low tide, nor is it easy to determine whether trees are mangrove or not. Best to be systematic So I follow my above rule, If in doubt, map as land.

- Corrections will come over the years, but slowly with local knowledge by different contributors. Other specialists may also join us, such as fishermen, who can help.

So:

At 05:46 AM 10/04/2009, Maning Sambale wrote:

>Some questions:
>
>1) How do we map mangrove [2] areas along coastlines?  In the "field"
>mangroves are either inland extending to the coast and even beyond
>coastline.  Do we include mangroves in inter-tidal areas as part of the
>coastline?

Map as land as it is easier. In the field, mangroves can be gradually identified and allow future mappers wiser than me to change that decision.


>2) Where do coastline and large rivers converge?  River deltas [3] is
>particularly problematic.

I try to imagine what a large scale silhouette map of just coastline would look like.  Would I be able to tell that there is a small, large river or delta there rather than a smooth coastline?  I then extend the coastline just enough inland to answer that question. A tiny nick for a small river.  A kilometre or so for a big estuarine one. For deltas, not easy. I pick one large channel at each side and map the coastline as that with anything in between as islands or islands with rivers, and anything "inland" as rivers.


>3) Sand bars? Siltation areas?  Any suggestions on how we map this?

If in doubt, map as land. Where absolutely sure, experiment with new tags such as "subsea="


>Me thinks: coastlines will never be complete because we have so much
>coastline and the threat of sea-level rise due to climate change