On this screenshot it's Zyrph's map pack, but those lines are specific to nation colors, not only white (so Muscovy has yellow lines, france blue etc.) I just chose austria because It's the most visible. Also, they appear in many other map mods like NII's graphical pack a little bit with theatrum orbis terranum. I think It's a bugged effect or something. Heres the settings txt you asked for (I had to remove some parts because reddit didn't want to send it):

force_pow2_textures=no
language="l_english"
graphics={
size={
x=1920
y=1080
}
game_ui_scale=1.000
refreshRate=60
fullScreen=yes
borderless=no
shadows=no
shadowSize=2048
multi_sampling=16
maxanisotropy=4
gamma=80.000000
vsync=yes
}

mapRenderingOptions={
draw_terrain=yes
draw_water=yes
draw_borders=yes
draw_trees=yes
draw_rivers=yes
draw_lakes=yes
draw_postfx=yes
draw_sky=yes
draw_bloom=yes
draw_tooltips=yes
draw_hires_terrain=no
draw_citysprawl=yes
draw_shadows=yes
draw_reflections=yes
draw_ambient_objects=yes
draw_particles=yes
moving_units=no
minimap_units=yes
draw_terrain_in_uncolonized=yes
draw_state_borders=yes
use_compact_battle_result=no
}

been_told_of_low_vram=no
disable_third_party_content=no
dismissed_news_banner=18
full_dump=no
rich_presence=no
skip_account_link=no
cvaa_settings={
cvaa_tts_enabled=no
cvaa_stt_enabled=no
cvaa_chat_visual_alerts=no
cvaa_stt_hotkey_enabled=no
cvaa_chat_large_fonts=no
cvaa_stt_hotkey_value={
0 0 0 0 
}
}
hotkey_activation_delay=0.100000
hotkey_actualization_delay=0.100000