I have a shapefile containing polygons (area of mangrove) per year for 35 years (=35 shapefiles). I would like to map changes of mangrove extent over time.
I want to map gains and losses (colour coded) between 1984 and 2019.
For overall change, I have been trying to union the mangrove_2019 with mangrove_1984, creating a field 'difference' and calculate the difference area. Though I can't figure out how to union layers based on a corresponding field/column. And then I want to somehow visualise the gains and losses - perhaps by categorising the positive and negative observed changes and then symbolising these? Though this is not exactly working for me.
For yearly changes, my only idea is to rasterise the dataset first. But I've tried to do this and my output raster is blank.
Any guidance/resources would be much appreciated.