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I've converted a shapefile (points) to KML with QGIS. Points in the shapefile are within 100m distance from each other. When I measure it in Google Earth, the distance changes to 80m. The same happens with the created GPX file. Why is this?

My original shapefile was created in WGS84/UTM Zone 20S because I needed to work with the metric system. I'm working with data belonging to an area no larger than 6 square kilometers. As to avoid the problem I am having now, I reprojected it to WGS84 (EPSG 4326) by "saving as" and changing its SRC before I then created the KML and GPX. Both KML and GPX show the same surface, the difference comes along with the shapefile.

Sample coordinates are:

    id  lat long
POINT(-61.82795607536099425 -37.83722374457502724)  
POINT(-61.82861595101069696 -37.83772772712714527)  
POINT(-61.82724009148368083 -37.83767676392982793)  
POINT(-61.8278967620074269 -37.83817748597036257)   
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    What projection/coordinate system is your original shapefile in? You may be getting odd results if you are trying to do a planar measurement on geodetic data (flat surface vs. curved surface). – Evil Genius Jul 8 '14 at 19:57
  • Following on what Evil Genius said, KML is supposed to have a standard projection (EPSG:4326), so if your GPS data is using a different projection and you haven't reprojected when creating the KML, the resulting file won't load in the right place. Related question (along with all the Related questions there). – Chris W Jul 8 '14 at 21:28
  • My original shapefile was created in WGS84/UTM Zone 20S because i needed to work with metric system. As to avoid the problem i am having now, i reproyected it to WGS84 (EPSG 4326) before i created KML and GPX. Both, KML and GPX show the same surface, the difference comes along with the shapefile. Thank you both. Please continue with your opinions. – lola Jul 9 '14 at 18:43
  • It may then be a function of what @EvilGenius said - your original data was in a projected CRS, and Google Earth uses a geographic CRS. I'm not a projections expert so I can't say right off. I'll edit your tags a bit and see if that doesn't attract one of them. You may want to edit your question to say exactly how you reprojected, as that may be relevant. – Chris W Jul 9 '14 at 23:57
  • Also, since you are using UTM, is all of your data within the zone? UTM has more distortion further away from the center of the zone. Some overlap is possible, but that may also be part of the problem if your points are actually in zone 19S or 21S. – Evil Genius Jul 10 '14 at 11:16
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If your points are in UTM zone 20S, lat and lon should be swapped.

Reprojecting the coordinates to UTM 20S, I get the following x-y coordinates:

id;lat;long;x;y
1;-37,83722374;-61,82795608;603131;5811597
2;-37,83772773;-61,82861595;603072;5811542
3;-37,83767676;-61,82724009;603193;5811546
4;-37,83817749;-61,82789676;603135;5811492

The distance from one point to the next is 80.66 meters. If your original shapefile had coordinates of 100m distance, there must have something been wrong with the first reprojection you did.

Perhaps you should add the coordinates in the original projection too.

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