diff --git a/R/PlotEquiMap.R b/R/PlotEquiMap.R
index 3de30e984afe36fdd29b1ece13069d5f67abd1d1..9981ed3bd7fdd190f7151977b040da13ce7b8b2a 100644
--- a/R/PlotEquiMap.R
+++ b/R/PlotEquiMap.R
@@ -847,9 +847,19 @@ PlotEquiMap <- function(var, lon, lat, varu = NULL, varv = NULL,
   col_inf_image <- ifelse(is.null(col_inf), colNA, col_inf)
   col_sup_image <- ifelse(is.null(col_sup), colNA, col_sup)
   if (square) {
-    image(lonb$x, latb$x, var[lonb$ix, latb$ix], col = c(col_inf_image, cols, col_sup_image), 
-          breaks = c(-.Machine$double.xmax, brks, .Machine$double.xmax),
-          axes = FALSE, xlab = "", ylab = "", add = TRUE)          
+    # If lat and lon are both regular-spaced, "useRaster = TRUE" can avoid
+    # artifact white lines on the figure. If not, useRaster has to be FALSE (default)
+    tryCatch({
+      image(lonb$x, latb$x, var[lonb$ix, latb$ix], 
+            col = c(col_inf_image, cols, col_sup_image), 
+            breaks = c(-.Machine$double.xmax, brks, .Machine$double.xmax),
+            axes = FALSE, xlab = "", ylab = "", add = TRUE, useRaster = TRUE)
+    }, error = function(x) {
+      image(lonb$x, latb$x, var[lonb$ix, latb$ix], 
+            col = c(col_inf_image, cols, col_sup_image), 
+            breaks = c(-.Machine$double.xmax, brks, .Machine$double.xmax),
+            axes = FALSE, xlab = "", ylab = "", add = TRUE)
+    })
   } else {
     .filled.contour(lonb$x, latb$x, var[lonb$ix, latb$ix], 
                     levels = c(.Machine$double.xmin, brks, .Machine$double.xmax),