Moderator: HAZ - Moderators
I don't understand . What is the current declination you mention? and are you saying that you are finding that the official declination noted on the Topo Maps is sometimes not correct?Nighthiker wrote:Though I have a lot of USGS topo maps that I utilize, I use the current declination and not what is labeled on the maps.
Most maps include an annual rate of change. It's pretty slow, though, especially compared to scale resolution and manual pointing error.Grasshopper wrote:I don't understand . What is the current declination you mention? and are you saying that you are finding that the official declination noted on the Topo Maps is sometimes not correct?Nighthiker wrote:Though I have a lot of USGS topo maps that I utilize, I use the current declination and not what is labeled on the maps.
Your discussion and this NOAA- Magnetic Declination Estimated Value link you note is interesting. Plugging in my residence zip code, I have learned that my GPS coordinate changes by 0° 6' W per year.. I had no idea!amy1300 wrote:You can get the current declination for a location by putting its latitude and longitude into the blanks at this site: ngdc.noaa.gov/geoma ... tion
Yeah, once I'd learned this I was kinda surprised the declination was printed on my map, without the year or any caution about it changing over time. You can bet I wrote in the current declination and the year, in the margin!Grasshopper wrote: The 3 degrees map declination "delta" you site in your reply narrative could be a big problem if you are lost (and not knowing about the 3 degree delta to add or subtract for your compass declination) and only have that map to use for your map and compass navigation to go from Point A (where you are lost) to Point B (where you hope to not be lost).
It's not much of a problem. Your GPS is pointing you to a location, not in a direction. If your GPS has an electronic compass in it, and the declination table is slightly off, you will start off in slightly the wrong direction. But as you walk, the pointer will keep correcting as you get nearer your destination. In essence, you will walk in a slight arc. In reality, you will likely be navigating around bigger obstacles like ridges, streams, and thickets that require excursions that dwarf the arc error. If your GPS does not have a compass, or the compass is shut off, or if you are moving fast enough, your GPS uses the change in your position over time to determine your direction of travel, and the earth's magnetic field isn't used at all.Grasshopper wrote:Now I'm wondering how the current declination for any location in my Garmin GPS (with the old 1:24k topo maps I have loaded for AZ,NM.UT,CO) are dealt with when using my GPS to navigate from one location to another?
I agree maps do offer many benefits over a GPS, but there are benefits of the GPS over a map as well... it's up to which is best for the individual.Nighthiker wrote: I prefer a map over a GPS because I can review a map and determine where I want to go while a GPS will tell me where to go.