diff --git a/README.md b/README.md
index 16c45167..6f5d1cf9 100644
--- a/README.md
+++ b/README.md
@@ -36,8 +36,8 @@ I don't know why 2.5 is the appropriate number, but the densities of many differ
 data sets fall off at about this same rate.
 
 For line features, it drops any features that are too small to draw at all.
-This still leaves the lower zooms too dark, so I need to figure out an
-equitable way to throw features away.
+This still leaves the lower zooms too dark (and too dense for the 500K tile limit,
+in some places), so I need to figure out an equitable way to throw features away.
 
 It also throws away any polygons that are too small to draw. I'm not sure yet
 if it is appropriate to do more than that.