Which coordinates are the best to use?

[+Northern Trekker]

When I place a cache, I try to be quite careful to get accurate coordinates.  I use my iPhone and I always let it settle into the coordinates for a good 2-3 minutes (reading 1).  Then I move away about 20 - 30 feet, then move back and do the same again (reading 2).  Finally I move off in a different direction and move back again (reading 3).  I take these 3 readings (which only vary by 0.001 at the most) and average them to get my final reading.

 

I then get home and plot the coordinates on google maps (same source maps as Geocaching), I see that my point is off on the map by up to 20 - 30 feet.  An example is if I were to place a cache at a lamp post in the middle of a parking lot (clear sky above, very little or no tree interference).  I can see on the map that the point is not at that lamp post, so I can correct the reading so that it is SPOT ON (usually, by adjusting both the northing and westing by up to 0.003 each.

 

My question is:  Which of these two coordinates is most accurate and should be used at the geocaching site?  

Example: Coordinates found on site with iPhone

 

Adjusted coordinates to be very close to the lamp post

[RuideAlmeida]

2 minutes ago, Northern Trekker said:

My question is:  Which of these two coordinates is most accurate and should be used at the geocaching site?  

 

 

Those you collected by yourself on the location.

[+niraD]

19 minutes ago, Northern Trekker said:

When I place a cache, I try to be quite careful to get accurate coordinates.  I use my iPhone and I always let it settle into the coordinates for a good 2-3 minutes (reading 1).  Then I move away about 20 - 30 feet, then move back and do the same again (reading 2).  Finally I move off in a different direction and move back again (reading 3).  I take these 3 readings (which only vary by 0.001 at the most) and average them to get my final reading.

 

I then get home and plot the coordinates on google maps (same source maps as Geocaching), I see that my point is off on the map by up to 20 - 30 feet.  An example is if I were to place a cache at a lamp post in the middle of a parking lot (clear sky above, very little or no tree interference).  I can see on the map that the point is not at that lamp post, so I can correct the reading so that it is SPOT ON (usually, by adjusting both the northing and westing by up to 0.003 each.

 

My question is:  Which of these two coordinates is most accurate and should be used at the geocaching site?  

The guidelines state, "The cache owner must visit the geocache location to get accurate coordinates with a GPS-enabled device." So as, RuideAlmeida wrote, use the coordinates you collected yourself with a GPS-enabled device at the actual location.

 

I used to live in an area where Google's satellite imagery was spot on, or at least calibrated as accurately as any consumer GPS device. But I always confirmed my coordinates with a GPS-enabled device at the actual location. And I've seen areas where it was off by significant distances, and I've seen the calibration error change when the satellite imagery is updated.

 

Anyway, if you don't trust your coordinates, then test them.

 

Enter your coordinates into your device, and then approach the cache location from at least 100ft/30m away. The arrow should point right at the cache location as you approach. Repeat the process, approaching the cache location from various directions, from at least 100ft/30m away each time. No matter which direction you approach from, the arrow should point right at the cache location.

 

If it doesn't, then adjust your coordinates until it does.

 

Bonus points for repeating the test on another day when the GPS satellites are in a different configuration.

 

Also, the Help Center article How to Get Accurate Coordinates should prove useful.
 

[+NanCycle]

Using the map coordinates to check that you haven't accidentally entered something wrong is a good idea, but the coordinates that you took on-site, especially if you did multiple readings, are the most accurate.  

[+CAVinoGal]

I follow the same process as you, though usually there are two of us taking readings with 2 different phones and a handheld GPS.  After verifying (or not) with Google maps, and especially if there is a significant difference such as you show, I go back another day and use the coordinates I took in the field and see how close they get me.  I use the GPS or phone coordinates, and only try to verify with Google maps, because that's not always accurate in my expereince.  It may get you close....but I feel more comfortable getting close with the device in my hand.  In most cases there isn't that much of a difference, and any comments on my coordinates have been that they are accurate.

[+SW00P]

I do what you do. Get coordinates then walk away and walk back. Sometimes 3 or 4 times. Then check Google maps to see if they match. Plus I open Wherigo app and use location function. 

 

In the end usually all are within 10 to 15 feet. Wherigo app is usually the best. I have an android phone. C:geo is app I use. 

 

If I struggle I give a strong hint.