Sit. Rep. #150: Map Legends and Scales

1- Map Scale seems to throw folks what the numbers mean and how to interpret the numbers.  The scale is simply a ratio of the size of the map to the size of geography (in the case of a USGS Topographic Map).  The scale on a 7.5-minute map is 1:24,000.  That number means that 1 inch on the map equals 24,000 inches of geography.

1B- You may see the scale as 1:25,000.  That is a metric-scaled map.  The numbers mean that 1 centimeter equals 0.25 kilometer.

Please note that the scale is perfect only at the center of the map.  Because we are looking at a flat, 2-dimensional map and the Earth’s Geography is curved; therefore the rest of the map is ever so slightly distorted.  I am being VERY, VERY technical with this note.

2- Usually the scale is found at the bottom of a map and is part of the map legend.  The legend is also called the Map Key.  The legend is, to me, every part of the map that is not part of the geography represented.  The USGS maps are surrounded by legend material on all 4 sides.  But the largest part of the legend (with the scale) is at the bottom of the map.  Sometimes the legend is on the reverse side of the map.  Read and be able to discern all of the legend’s references, words, marks, scales, and symbols.  Here is a link to the USGS Map Symbols.

3- The wording is a bit confusing but please bear with me (& USGS).  A Small Scale Map shows a larger geographic area.  A Large Scale Map shows a smaller geographic area but with much greater detail.  A Small Scale Map such as 1:100,000.  A Large Scale Map as 1:24,000.  A Small Scale Map shows fewer features.  Remember it this way:  Large Scale has many details.

Example:  You can have a Small Scale Map that shows all 48 contiguous states (of ~3.12 million square miles) on the same size sheet of paper as a Large Scale Topographic 7.5-minute map (it shows about 50 square miles).  Clear as mud?

4- Map colors are way more simple:  Note: Most maps that are “photo corrected” or “photometric” or Satellite maps, the photos used to make these maps and corrections are taken during the winter (most of the time).  Lakes may be drawn down, trees are without leaves, farmland barren.

  • Green – vegetation, such as trees, orchards, groves, marsh, tundra
  • Brown – contour lines, and relief features such as sand, strip mines, glaciers, dunes, levees, construction, cuts, ice fields
  • Blue – water, such as rivers, lakes, ponds, creeks, oceans, bays, marshes, swamps, streams
  • Black – man-made, such as buildings, cemeteries, houses, railroads, pipelines, power lines, lighthouses, roads, political boundaries, athletic fields,  (some) bathymetric contours, sea walls, jetties, shipwrecks, benchmarks, hiking trails, airports, and much more
  • Red – improved roads or major highways (such as Interstate Highways)
  • Purple or pink – updated section
  • Unusual marks – Glacial advance is marked in black.  Glacial retreat is marked in blue/green.

S: Mom I am nervous to cross over to Scouts tonight.
T: Don’t worry.  You have knotting to worry about.

5- Meeting Plans & Notes:
Map scale reading.
Get a state highway map.
Compare to USGS Topo Map.

U: Why are Scouts like a new pair of socks?
V: They come pre-paired.


On Santa’s knotty list,

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