Add places layer with population data

[trey-stafford]

As part of removing the HOTOSM layers (see #540), we removed a populated places layer that is used in tutorial materials.

We need to do one of the following:

• find an alternative source for this layer so that tutorial materials can continue to work
• re-add the HOTOSM layer (maybe the latest version has updates that address some of our original concerns?)
• Replace tutorial materials with new example that doesn't use the HOTOSM population layer. This might be difficult if this layer is featured on e.g., our beginner workshop. Will need to confirm.

[trey-stafford]

In any case, a layer containing the population field should make sure that the field is a number type, not string. There was an issue w/ v2 wherein the population field was a string, making the tutorial/exercise more difficult to complete.

[trey-stafford]

Related issue: #567

[trey-stafford]

When we add this data, we should consider using symbology which visualizes the cities/settlements by population size. From Jira:

Use symbol size or color to indicate population of towns/settlements.

We need to find a source for this data, as the "asiaq private placenames" source does not have it. I believe Eva Matzler produced that dataset for us manually.

[trey-stafford]

The new "Places/Towns" and "Places/Settlements" layers added for #553 in PR #570 have a population field.

Maybe we can adapt existing materials to use those layers instead of the previously used "Places/Community map (crowd-sourced)/Populated places" layer.

[trey-stafford]

The QGreenland Beginner's Tutorial Series, Session 5: Processing Toolbox and Data Analysis YouTube video pretty explicitly makes reference to the "Populated places" layer and that it is under the "Places/Community map (crowd-sourced)" group.

It also shows the attributes list from the "Populated places" layer, but only briefly and in the context of a processing toolbox tool dropdown.

The video also notes that the symbology for "Populated places" (the same we use for the new "Towns" and "Settlements" layers) is hard to see, especially when a selection is made with the "select by attributes" tool. Note above that we want to change the symbology.

Based on our team conversation this morning, a good path forward would be to:

• Combine the new "Towns" and "Settlements" layers into one "Populated places" layer.
  • Filter out places with a population of 0?
  • Update "Population 2016" field to be "population" (consistent with the field name in the original "Populated places" layer from HOTOSM)? This field gets referenced in the tutorial video. We could just note in the layer description that the population data is from 2016.
• Add note to tutorial video indicating that the video was made with QGreenland v2 and that v3 updated the "Populated places" layer and moved it to the root of the "Places" group.
• Update the symbology for the resulting combined layer (see above comment)

Although we haven't really built-in support for multi-asset layers yet, we do have at least one example where we have done so: the USGS earthquakes layer. This layer uses wget to fetch multiple parts of a larger dataset and then ogr_merge.py to combine them. A similar approach could work here.

[trey-stafford]

PR w/ initial changes to RTD tutorial text: https://github.com/nsidc/qgreenland/tree/update-tutorial-materials

I just subbed in "Towns" instead of "Populated places" so this will need to be updated again if the above plan is put into place.