`--keep` resulting in smaller file than `--keep-ways` using exact same filter with `osmfilter`

Help and support
1

I already asked this here but I doubt I’ll get any response soon:

I converted the morocco-latest PBF file from GeoFabrik to o5m using osmconvert. Then I ran the following two commands:

osmfilter --keep="boundary=administrative and admin_level=4" -o="AdminLevel4.osm" ..\morocco-latest.o5m

osmfilter --keep-ways="boundary=administrative and admin_level=4" -o="AdminLevel4Ways.osm" ..\morocco-latest.o5m

Surprisingly, AdminLevel4Ways.osm is a lot larger than AdminLevel4.osm. AdminLevel4Ways.osm is 3.8G while AdminLevel4.osm is 20.2M.

I was under the impression that all keep-ways would do is to filter out only the ways which have tags of boundary=administrative and admin_level=4, and leave out the relations which would result in a smaller file.

Am I doing something wrong here? Is my understanding of how osmfilter does the filtering flawed? Is this a known bug?

2

Welcome, I did read the wiki.

Can you try:

osmfilter --keep= --keep-ways="boundary=administrative and admin_level=4" -o="AdminLevel4Ways.osm" ..\morocco-latest.o5m

So add --keep=?