diff --git a/README.md b/README.md
index 15a8b18..bc2fb14 100644
--- a/README.md
+++ b/README.md
@@ -15,4 +15,9 @@ https://web.archive.org/web/20220421120137/https://wiki.openstreetmap.org/wiki/S
 https://wiki.openstreetmap.org/wiki/Slippy_map_tilenames
 https://en.wikipedia.org/wiki/Web_Mercator_projection
 https://web.archive.org/web/20141009142830/http://earth-info.nga.mil/GandG/wgs84/web_mercator/(U)%20NGA_SIG_0011_1.0.0_WEBMERC.pdf
-https://www.openstreetmap.org/#map=15/22.7602/114.3888&layers=D
\ No newline at end of file
+https://www.openstreetmap.org/#map=15/22.7602/114.3888&layers=D
+https://en.wikipedia.org/wiki/Eccentricity_(mathematics)#:~:text=The%20eccentricity%20of%20an%20ellipse%20is%2C%20most%20simply%2C%20the%20ratio,of%20the%20semimajor%20axis%20a.&text=(Flattening%20may%20be%20denoted%20by,if%20f%20is%20linear%20eccentricity.)
+
+http://wiki.gis.com/wiki/index.php/Geodetic_system
+https://developer.mozilla.org/zh-CN/docs/Web/API/CanvasRenderingContext2D/textBaseline
+https://developer.mozilla.org/zh-CN/docs/Web/API/CanvasRenderingContext2D/textAlign
\ No newline at end of file