Is it possible not default PDF for layers merging?

Version gmt 6.1 fro windows
Can not merge layers for formats exсept
pdp
When I make - png, -ps etc at end of commnadы,
I get pictures for each layer, no merging
For example following script gives me correct merged pdf
But I can not modify it to create same merged png or postsript
gmt begin map
gmt coast -R25.5/45.5/34.5/42.5 -JM6i -Gwhite -S0/200/255 -U -I9/0/0/255 -I1/0/0/255 -I2/0/0/255 -B
gmt xyz2grd cureqandtbl1.csv -R26/44/35/41.9375 -JM6i -I10k -Gtr.nc
gmt grdcontour tr.nc -JM6i -B -S4 -Ncont.cpt
gmt end show

You make layers via gmt being name formats. The -png and -pdf etc are for single-layer plots only.

Please, any sample
I am still very stupid in GMT

Probably something like this script:

gmt begin map png
gmt coast -R25.5/45.5/34.5/42.5 -JM6i -Gwhite -S0/200/255 -U -I9/0/0/255 -I1/0/0/255 -I2/0/0/255 -B
gmt xyz2grd cureqandtbl1.csv -R26/44/35/41.9375 -I10k -Gtr.nc
gmt grdcontour tr.nc -S4 -Ncont.cpt
gmt end show

It should create the PNG file map.png and open it for you to view.

No, it gives error message
gmt [ERROR]: Option -N: CPT file must be discrete, not continuous
and only one png file with coast

thank a lot
It was my mistake
with cpt
script works fine !!
and produce png merged file
gmt begin map png
gmt coast -R25.5/45.5/34.5/42.5 -JM6i -Gwhite -S0/200/255 -U -I9/0/0/255 -I1/0/0/255 -I2/0/0/255 -B
gmt xyz2grd cureqandtbl1.csv -R26/44/35/41.9375 -I10k -Gtr.nc
gmt grdcontour tr.nc -S4
gmt end show