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EGMaps – Clean Up Your Data

Now that you’ve collected your data, it may need to be cleaned up on your computer.  This is usually done in the software that came with your GPS.  Good, free, programs are available for this from GPS manufacturers and others.  They all basically do the same thing, but do it in different ways.  If you have one you know, use it.  If not, download a few and see which one seems most natural to you.

If you’re only using POI’s, then you can probably just double-check that they all point where they’re supposed to and that there aren’t any extra.  If you’re using trails, though, you’re going to need to do a bit more work.

Consolidate your data

If you’re working with a large trail network, you probably collected the data over several days, weeks, even months or more.  Use your computer-based GPS data editing program to bring all your data together into a single file.

Chop up your trails into segments

When you collected your data, you probably started a trail at the parking lot, hiked all over the place, through intersections, criss-crossing your own track, and finally ending back at the parking lot (or your home, if you forgot to turn off the GPS).  Now you need to cut up the trail into multiple segments or tracks.  Exactly where you cut the trail is up to you, but remember that you’ll need a separate segment if you want a separate color, and you’ll need separate segments for favorite trails, too.  Generally, the best places to cut your original trails into segments include (but are not limited to):

  • Parking areas
  • Intersections
  • Destinations (if a favorite trail will end there, instead of continuing)

You can usually name your segments.  Do it!  This will make it far, far easier to assemble the segments into favorites later.  Don’t hesitate to set colors, either, perhaps one color for paved trails and another for dirt, or a color for each of what will eventually turn into a favorite route.  Naming them will also make it easier to which trails you haven’t worked with yet.

Simplify your data

Your GPS collected too much data.  Your app users don’t want it all.  It takes too much work, takes too long to load, and takes up too much space.  The good news is, you can probably get rid of about 75% of it without anyone even noticing.  Here’s how.  Start with your first segment, and progress segment to segment.  For each segment:

  1. On straight areas, you really only need a track point at each end.  You don’t need any points at all in the middle.  Delete the extras.
  2. For curves, you can probably get rid of usually get rid of points closer than five, or even ten meters.  You want to retain the general shape of the curve, but remember that smartphone users won’t have the same resolution as your PC.  We usually get rid of at least half the points along curves, and usually more like three quarters of them.  App users never see that the data is gone, but they do see faster load times, less space usage, and a better app.


Get rid of duplicates

Wouldn’t it be great if you could hike each trail segment exactly once?  If you have a fairly simple trail network, maybe you can, but if it picks up even a little complexity, chances are you’re going to have to hike some of the same sections over and over.  You don’t want those in your app.  Zoom in on your data and find those duplicates and delete them.

Fix the intersections

Even the best hiking GPS is accurate to only a few meters.  This means that when I pass trail marker #3 four times, it’ll show four different points in the data.  The trails won’t all naturally intersect exactly, and the trail points even less so.  Edit your trails to make all the trails actually intersect at the same point.  This usually means editing both the start and end point of each of your trail segments.  Don’t worry about being exactly on, but you should try to get within a meter or so.  If it visually looks like it’s in the same place while you’re fully zoomed in, that’s good enough.

Put together the ends

Depending on your GPS, and how long you go on each survey session, your GPS may have cut up your data mid-trail.  By now, you should be able to see where these multiple pieces are and you can stick them together into single segments. Technically, you don’t really have to do this, but it does make it a bit easier later on.

Export your data

Depending on what program you’re using, you need to export it to a form you can edit more directly.  Probably this will be either GPX or XML.

Now it’s time to format your data so EGMaps can use it.

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