Map on this website

Discussion in 'Electronics Insanity' started by mudboy dave, Apr 10, 2019.

  1. mudboy dave

    mudboy dave Explorer

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    when you go to "Maps" at the top of this page, there is the "topo" option. As you zoom in it obviously becomes more clear, it also appears to change maps. at what scale is the most zoomed in? in example 1:24000? i would like to purchase some paper maps to that detail but am not quite sure what to order.
    Thanks,
    Dave
     
  2. Boyd

    Boyd Super Moderator
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    These are the same maps that were marketed for many years by National Geographic under the TOPO! product name. They now belong to ArcGIS and are offered online here:

    https://www.arcgis.com/home/webmap/viewer.html?webmap=931d892ac7a843d7ba29d085e0433465

    National Geographic took the USGS 24k topo maps and added shaded terrain to give them a more three-dimensional look. AFAIK, they were never offered on paper, they were originally sold on DVD for use on Windows computers and Magellan handheld GPS units.

    Regarding the map change as you zoom , look at the address bar in your web browser and note the part with "z=". That number is the "zoom level". The arcGIS topos are configured to show a 100k topo map when you zoom out to level 13 (z=13) or smaller. When you zoom to level 14 or higher (z=14) then a 24k topo is shown.

    The term "24k" is shorthand for a map scale of 1:24,000, so, 1 inch on the map equals 24,000 inches (2,000 feet) in the real world. With a 100k map, 1 inch equals 100,000 inches (about 8,000 feet) in the real world. The 24k topo maps are often called 7.5 minute top maps. This terminology refers to the system where coordinates were specified with degrees, minutes and seconds - like an old analog clock. A minute is 1/60 of a degree. Therefore, 7.5 minutes represents 1/8 of a degree, which defines how much area each topo map covers. This is called a "quadrangle".

    So this is probably a lot more than you really wanted to know about maps, but the concepts are pretty important. :) You can purchase the paper USGS 7.5 minute topo maps here. There are probably other sources. They used to sell them at the Batsto visitor center, not sure if they still do. REI also used to sell them.

    https://store.usgs.gov/filter-products?categories=[15]&page=1

    For a free, high quality downloadable version that you can use on your GPS or phone, see my "1999 in the Pines" map. You will also find a number of other historical topo maps on my site.

    https://boydsmaps.com/1999-in-the-pines/

    Note that the USGS discontinued the 7.5 minute topo's almost 20 years ago, so they are now consided "historical maps". Many of the NJ quadrangles have not been updated for 50 years or more, so quite a few things have changed. Here's an index that shows all the quadrangle names for South Jersey. The dates that are shown are the most recent versions available, and these are what I used for "1999 in the Pines".

    BTW, the free Mobile Atlas Creator that is used for my maps also has a function to print hard copies (although I have never tried).

    1999coverage.png
     
    #2 Boyd, Apr 10, 2019
    Last edited: Apr 10, 2019