diff --git a/Dev-Notes.md b/Dev-Notes.md
index 17a849a..2d77da3 100644
--- a/Dev-Notes.md
+++ b/Dev-Notes.md
@@ -43,10 +43,12 @@ Next steps:
 Elevation data tutorials/resources:
 
 - https://opensourceoptions.com/how-to-download-lidar-dems-digital-elevation-models-and-point-clouds-from-the-usgs/
-- https://apps.nationalmap.gov/downloader/#/ (where to get DEMs from, no account needed)
+- https://apps.nationalmap.gov/downloader/#/ (where to get DEMs, no account needed)
 - https://www.geodose.com/2017/08/how-to-use-arcgis-rest-api-service-qgis.html (how to get terrain in QGIS)
 - https://www.geodose.com/2018/02/dem-3d-visualization-qgis.html (excellent tutorial, assume you have DEMs already)
 
+3D maps need to be in a "projected" geography like Mercator, not spheroid like WGS-84.
+
 ## 20240117
 
 Example SQL query to create a `qgis_friendly` view that converts Cayenne GPS location into PostGIS point, includes unique ID, RSSI, time, and gatewayId, and filters on gatewayId: