going up in the world

Cumulative Ascent...

... aka Cumulative Elevation Gain or Vertical Variation, of a route is the sum of all the ascents, ignoring the descents.  It is important in judging the difficulty of the walk or ride.

To compare two routes of different lengths and cumulative ascents, it helps to convert the ascent to a distance on the flat that would be equally arduous.  

Cycling

For cycling, the conversion depends on how fast you cycle on the flat.  Assuming no wind, I use the following:

Walking

For walking, use 1:10; a 1m elevation gain costs about the same as 10m on the flat.

Obtaining the elevation data

Many GPX files are generated by someone traversing the route while carrying a device which takes signals from satellites to find its latitude and longitude.  It records these for many points ("waypoints") along the route.  Some devices use barometric altimeters or satellite signals to determine the elevations and record those too.

Be wary of DEM

Often, however, GPX files are created with only latitude and longitude data, no elevations.

Tools are freely available which will fill the elevation data in from public Digital Elevation (DEM) data using the coordinates from the GPX file, but the DEM data cannot be expected to hold elevation values for every possible waypoint.  The elevation value used will be for somewhere near the waypoint.  The best publicly available data (NASA/USGS) has datapoints every arc second NS and EW.  That's about every 30m NS and, around Sydney, every 25m EW.

If the road is flanked by a steep slope, and the nearest DEM datapoint to the waypoint is on that slope, this can produce false jumps in elevation and grossly inflated cumulative ascents.

In rugged country, it is not unusual for the cumulative ascent so calculated to be as much as twice the true value.

More than once, a cycle tour operator has sent me GPX files containing DEM elevations, together with cumulative ascent numbers that have been derived from them more-or-less uncritically.  If the values quoted were correct I would have been physically incapable of the ride - or unnecessarily opted for an e-bike.

Some operators moderate the quoted cumulative ascent by applying a threshold to the elevation changes, ignoring all those below the threshold.  That is no solution since it completely misunderstands the problem.  In effect, you have to know the right answer and tweak the threshold until you get it! 

How to solve this

For cycling

More reliable numbers can be obtained by recreating the route in Google Maps.  Mostly, Google Maps makes better estimates of the elevations, but it is not perfect.  Unfortunately, recreating the route can be arduous.  Google Maps knows exactly where roads are but cannot figure the route out from GPX waypoints.  So get Google Maps to pick its own route* from the start point to the finish point, then adjust it as necessary until it follows your intended route.  The distance it then shows is only for the first leg - you need to select each leg in turn to see its total length - but it does show a reasonably correct cumulative ascent number for the whole trip.

For walking

The above may also work for walking, but Google Maps will often be ignorant of the tracks you have in mind.

*Tip: Planning cycle routes from scratch with Google Maps is tricky because it has a nasty habit of selecting tracks you'd need a BMX for.  Always verify using Street View or pretend that you will be driving to force it to use decent roads.