Description kat1024_assets is a zip file only so content needs to be extracted into your ..aseq3 folder before the included *.map file can be opened in Quake 3's editor (GTK, QeRadiant etc..)
The new multiplant pack fixes a number of bugs and issues in the oA small 1024x1024 'terrain' map including *.map file sample map and editor assets to accumpany the 'modelling a map tutorial' here.