Accurate Miles on Longer Races
Recently did GPS measurement of a half marathon and faced old problem of low resolution of miles running the arrow across an Elevation Profile: 1/100 of a mile is bad enough but after 10 miles all I know how to see is 1/10 of a mile or about 161 meters.
Backing up a minute, to approximate a bike measurement, I multiply the course distance by 1.0014: for a half marathon that is 21,127 meters. This is usually a little conservative but fear of running out of road for a turnaround is deeply ingrained.
Next, I would do a tight plot which means a rough plot followed by refinements. At this point, I used to run an Elevation Profile and slid the arrow across. Finally, it occurred to me that, I could use the Properties function, select Meters from the Measurement tab and work back. So I did a spreadsheet of 21,127 * Mile mark / 13.1093 like 21,127 * 13 / 13.1093 = 20,950.8.
Next, I VERY CAREFULLY saved a KMZ of the overall plot and renamed the one I had something ending in MileFind. This one I could destroy and always start over from the full original plot.
So then was just a matter of deleting all the points going backward and adjusting each mile to the exact desired # of meters as you come to it. If nothing else, it will be consistent. From here, pictures will wotk best in the field to help you find where mile marks should be.