Polygonize.py outputs into a single file or simple merge?

Question

Given an unique raster topographic file at start, I want to get vector polygons for elevations thresholds 1m, 200m, 500m, 1000m, 2000m into a single shp file. I first slice my raster into 5 (or more) rasters, then polygonize each, and then have to merge them.

How to get these outputs into a single shape file ? Either by sending them as layers directly into the same file, or by creating individual shp files to merge into one final shp.

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Current workflow details: It seems I must do this because poligonize works on pixels with a same value (elevation) x.

1. Generate raster slices: I used gdal_calc.py to generate kinds of vertical slices, with one .tif for each level :

gdal_calc.py -A crop.tif --outfile=level001.tif --calc="1*(A>0)"     --NoDataValue=0
gdal_calc.py -A crop.tif --outfile=level200.tif --calc="200*(A>200)" --NoDataValue=0
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All conserved pixels in level001.tif have an elevation of 1. All conserved pixels in level200.tif have an elevation of 200m. Opened together in QGis it give slices like this:

2. Polygonize my rasters slices (files):

I run polygonize.py separatedly on each of these several raster files to get my vector layers:

gdal_polygonize.py level001.tif -f "ESRI Shapefile" levels001.shp levels001 elev
gdal_polygonize.py level200.tif -f "ESRI Shapefile" levels200.shp levels200 elev
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3. Merge into one shp file.

How to merge these shp outputs ?

Alternatively, I'am also interested by smoother workflow (loop).

Answer 1

If the shapefiles to be merged are in the same directory:

ogr2ogr merge.shp levels001.shp
ogr2ogr -update -append merge.shp levels200.shp -nln merge
ogr2ogr -update -append merge.shp levels500.shp -nln merge
ogr2ogr -update -append merge.shp levels1000.shp -nln merge
ogr2ogr -update -append merge.shp levels2000.shp -nln merge