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My question is in the same vein as this one.

I'm attempting to convert precipitation lines (Precipitación Media Anual) to a polygon for Mexico in QGIS using the Polygonizer plugin.

After running the Polygonizer using the New Method, it returns the polygon but with a table full of NULL values after clicking Copy table field from line layer, the same as this problem.

The Old Method crashes at around 19% completion.

Here's a few related questions to this problem:

Is clipping the lines to smaller sizes the easiest option?
extracting each line class, polygonize, and then union
Though I'm unfamiliar with GRASS, is there a way to easily do this?

EDIT: I'm going to see if GRASS or PostGIS will do the trick

I'm open to any other ways to do this.

Thanks again for all the help!

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