Fortunately, you may redefine structure of maps anytime. The "layers structure" works for me.
An example: map CJ_layers.map CJ_1layer.map break CJ_2layer.map break CJ_3layer.map endmap map CJ_1layer.map pod_vchodom.map@pod_vchodom priepastovy_kaplnka.map@priepastovy_kaplnka osviezovna.map@osviezovna meander.map@meander zlty_dom.map@zlty_dom jarine_domy_cele.map@jarine_domy_cele oranzovy.map@oranzovy preview below CJ_2layer.map preview below CJ_3layer.map endmap map CJ_2layer.map zabkin_dom.map@zabkin_dom velka_puklina.map@velka_puklina vp_vd.map@vp_vd FAJCIAR_CELY.map@FAJCIAR_CELY biely_dom_cely.map@biely_dom_cely bordel.map@bordel dom_starcov.map@dom_starcov sup_cely.map@sup_cely preview above CJ_1layer.map preview below CJ_3layer.map endmap map CJ_3layer.map STARA_CESTA_MAPA.map@STARA_CESTA_MAPA sup_dno.map@sup_dno brckova_chodba.map@brckova_chodba rotunda_cela.map@rotunda_cela perlovy.map@perlovy preview above CJ_1layer.map preview above CJ_2layer.map endmap