The combination of trails and strokeTrail produces artifacts in the rasterific backend but not the SVG backend. There are lines going across the fill for the PNG but the SVG is completely solid. I've attached a minimal example below.
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE NoMonomorphismRestriction #-}
{-# LANGUAGE TypeFamilies #-}
module Artifact where
import Data.Aeson
import Data.Vector (Vector)
import qualified Data.Vector as V
import Diagrams.Backend.Rasterific
import Diagrams.Backend.SVG
import Diagrams.Prelude
test :: IO ()
test = do
renderSVG "wyoming.svg" (dims (V2 1000 1000)) mkDia
renderRasterific "wyoming.png" (dims (V2 1000 1000)) mkDia
mkDia = (map p2 pts)
# fromVertices
# closeTrail
# strokeTrail
# fc blue
# bgFrame 1 white
pts :: [(Double, Double)]
pts = [(-109.050076,41.000659),(-109.173682,41.000859),(-109.231985,41.002059),(-109.250735,41.001009),(-109.500694,40.999127),(-109.534926,40.998143),(-109.676421,40.998395),(-109.713877,40.998266),(-109.715409,40.998191),(-109.854302,40.997661),(-109.855299,40.997614),(-109.97553,40.997912),(-109.999838,40.99733),(-110.000708,40.997352),(-110.006495,40.997815),(-110.121639,40.997101),(-110.125709,40.99655),(-110.237848,40.995427),(-110.250709,40.996089),(-110.375714,40.994947),(-110.500718,40.994746),(-110.539819,40.996346),(-110.715026,40.996347),(-110.750727,40.996847),(-111.046723,40.997959),(-111.046551,41.251716),(-111.0466,41.360692),(-111.046264,41.377731),(-111.045789,41.565571),(-111.046689,42.001567),(-111.047109,42.142497),(-111.047107,42.148971),(-111.047058,42.182672),(-111.047097,42.194773),(-111.047074,42.280787),(-111.04708,42.34942),(-111.046801,42.504946),(-111.046017,42.582723),(-111.043564,42.722624),(-111.044135,42.874924),(-111.043959,42.96445),(-111.043957,42.969482),(-111.043924,42.975063),(-111.044129,43.018702),(-111.044206,43.022614),(-111.044034,43.024581),(-111.044034,43.024844),(-111.044033,43.026411),(-111.044094,43.02927),(-111.043997,43.041415),(-111.044058,43.04464),(-111.044063,43.046302),(-111.044086,43.054819),(-111.044117,43.060309),(-111.04415,43.066172),(-111.044162,43.068222),(-111.044143,43.072364),(-111.044235,43.177121),(-111.044266,43.177236),(-111.044232,43.18444),(-111.044168,43.189244),(-111.044229,43.195579),(-111.044617,43.31572),(-111.045706,43.659112),(-111.04588,43.681033),(-111.046118,43.684902),(-111.046051,43.685812),(-111.04611,43.687848),(-111.046421,43.722059),(-111.046435,43.726545),(-111.04634,43.726957),(-111.046715,43.815832),(-111.046515,43.908376),(-111.046917,43.974978),(-111.047349,43.999921),(-111.049077,44.020072),(-111.048751,44.060403),(-111.048751,44.060838),(-111.048633,44.062903),(-111.048452,44.114831),(-111.049119,44.124923),(-111.049695,44.353626),(-111.049148,44.374925),(-111.049216,44.435811),(-111.049194,44.438058),(-111.048974,44.474072),(-111.055208,44.624927),(-111.055511,44.725343),(-111.056416,44.749928),(-111.056888,44.866658),(-111.055629,44.933578),(-111.056207,44.935901),(-111.055199,45.001321),(-111.044275,45.001345),(-110.785008,45.002952),(-110.761554,44.999934),(-110.750767,44.997948),(-110.705272,44.992324),(-110.552433,44.992237),(-110.547165,44.992459),(-110.48807,44.992361),(-110.402927,44.99381),(-110.362698,45.000593),(-110.342131,44.999053),(-110.324441,44.999156),(-110.28677,44.99685),(-110.199503,44.996188),(-110.110103,45.003905),(-110.026347,45.003665),(-110.025544,45.003602),(-109.99505,45.003174),(-109.875735,45.003275),(-109.798687,45.002188),(-109.75073,45.001605),(-109.663673,45.002536),(-109.574321,45.002631),(-109.386432,45.004887),(-109.375713,45.00461),(-109.269294,45.005283),(-109.263431,45.005345),(-109.103445,45.005904),(-109.08301,44.99961),(-109.062262,44.999623),(-108.578484,45.000484),(-108.565921,45.000578),(-108.500679,44.999691),(-108.271201,45.000251),(-108.249345,44.999458),(-108.238139,45.000206),(-108.218479,45.000541),(-108.14939,45.001062),(-108.000663,45.001223),(-107.997353,45.001565),(-107.750654,45.000778),(-107.608854,45.00086),(-107.607824,45.000929),(-107.49205,45.00148),(-107.351441,45.001407),(-107.13418,45.000109),(-107.125633,44.999388),(-107.105685,44.998734),(-107.084939,44.996599),(-107.074996,44.997004),(-107.050801,44.996424),(-106.892875,44.995947),(-106.888773,44.995885),(-106.263586,44.993788),(-105.928184,44.993647),(-105.914258,44.999986),(-105.913382,45.000941),(-105.848065,45.000396),(-105.038405,45.000345),(-105.025266,45.00029),(-105.019284,45.000329),(-105.01824,45.000437),(-104.765063,44.999183),(-104.759855,44.999066),(-104.72637,44.999518),(-104.665171,44.998618),(-104.663882,44.998869),(-104.470422,44.998453),(-104.470117,44.998453),(-104.250145,44.99822),(-104.057698,44.997431),(-104.055914,44.874986),(-104.056496,44.867034),(-104.055963,44.768236),(-104.055963,44.767962),(-104.055934,44.72372),(-104.05587,44.723422),(-104.055777,44.700466),(-104.055938,44.693881),(-104.05581,44.691343),(-104.055892,44.543341),(-104.055927,44.51773),(-104.055389,44.249983),(-104.054487,44.180381),(-104.05495,43.93809),(-104.055077,43.936535),(-104.055488,43.853477),(-104.055138,43.750421),(-104.055133,43.747105),(-104.054902,43.583852),(-104.054885,43.583512),(-104.05484,43.579368),(-104.055032,43.558603),(-104.054786,43.503072),(-104.054766,43.428914),(-104.054614,43.390949),(-104.054403,43.325914),(-104.054218,43.30437),(-104.053884,43.297047),(-104.053876,43.289801),(-104.053127,43.000585),(-104.052863,42.754569),(-104.052809,42.749966),(-104.052583,42.650062),(-104.052741,42.633982),(-104.052586,42.630917),(-104.052775,42.61159),(-104.052775,42.610813),(-104.053107,42.499964),(-104.052776,42.25822),(-104.052793,42.249962),(-104.053125,42.249962),(-104.052761,42.170278),(-104.052547,42.166801),(-104.053001,42.137254),(-104.052738,42.133769),(-104.0526,42.124963),(-104.052954,42.089077),(-104.052967,42.075004),(-104.05288,42.021761),(-104.052729,42.016318),(-104.052699,41.998673),(-104.052761,41.994967),(-104.05283,41.9946),(-104.052856,41.975958),(-104.052734,41.973007),(-104.052991,41.914973),(-104.052931,41.906143),(-104.053026,41.885464),(-104.052774,41.733401),(-104.052913,41.64519),(-104.052945,41.638167),(-104.052975,41.622931),(-104.052735,41.613676),(-104.052859,41.592254),(-104.05254,41.564274),(-104.052531,41.552723),(-104.052584,41.55265),(-104.052692,41.541154),(-104.052686,41.539111),(-104.052476,41.522343),(-104.052478,41.515754),(-104.05234,41.417865),(-104.05216,41.407662),(-104.052287,41.393307),(-104.052687,41.330569),(-104.052324,41.321144),(-104.052476,41.320961),(-104.052568,41.316202),(-104.052453,41.278202),(-104.052574,41.278019),(-104.052666,41.275251),(-104.053514,41.157257),(-104.053142,41.114457),(-104.053083,41.104985),(-104.053025,41.090274),(-104.053177,41.089725),(-104.053097,41.018045),(-104.053158,41.016809),(-104.053249,41.001406),(-104.066961,41.001504),(-104.086068,41.001563),(-104.10459,41.001543),(-104.123586,41.001626),(-104.211473,41.001591),(-104.214191,41.001568),(-104.214692,41.001657),(-104.467672,41.001473),(-104.497058,41.001805),(-104.497149,41.001828),(-104.675999,41.000957),(-104.829504,40.99927),(-104.855273,40.998048),(-105.254779,40.99821),(-105.256527,40.998191),(-105.277138,40.998173),(-105.724804,40.99691),(-105.730421,40.996886),(-106.061181,40.996999),(-106.217573,40.997734),(-106.321165,40.999123),(-106.386356,41.001144),(-106.391852,41.001176),(-106.43095,41.001752),(-106.437419,41.001795),(-106.439563,41.001978),(-106.453859,41.002057),(-106.857773,41.002663),(-107.000606,41.003444),(-107.241194,41.002804),(-107.367443,41.003073),(-107.625624,41.002124),(-107.918421,41.002036),(-108.046539,41.002064),(-108.181227,41.000455),(-108.250649,41.000114),(-108.500659,41.000112),(-108.526667,40.999608),(-108.631108,41.000156),(-108.884138,41.000094),(-109.050076,41.000659)]