I am building a uMap of local bike infrastructure, including lanes. I use the polyline tool to draw bike lanes on the map. To mass edit data on a layer including these lanes, I exported a CSV, made some adjustments, and re-imported. On re-import, all the drawn lines were overwritten and replaced with single-point dots.
When working with uMap, is there a way to export/import layer data as a CSV when a layer contains polylines, without destroying those lines in the process?
You have to use wkt if you want CSV-compatible format but which preserves lines.
Or of course one of gpx, geojson or kml (which I would recommend instead for their popularity and availability of tools to handle them).
csv AFAICT stores just a list of points, with no information about how they are interconnected. So, that which is not saved, cannot be restored either.
Thank you! I will experiment with those other filetypes.
I had been using the CSV export/import to be able to view the data in an Excel spreadsheet for easier mass editing of some elements. Would a WKT file serve that purpose?
It depends on the nature of mass editing I guess. 
But yes, Excel will open WKT CSV file just like any other CSV file.
The difference is that you’ll have one-row-per-polyline in WKT format, instead of one-row-per-point as you had with “bare” CSV export.
I guess it would be easiest if you just try it out and see if it works for you.