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I've got a problem that I am sure at least one of you have dealt with. I'm new to a company that makes use of a rather large database of point data. For whatever reason, the woman who was here before me made a huge amount of duplicate points - the attributes may be a little different but the coordinates are the same.

I've found that I can remove the points either in QGIS using the mmqgis plugin, or in ArcMap using the "delete identical" tool. However, when I use either method, I have noticed that there are some points that are removed completely. For most, it leaves one point but I have found a few that are completely gone.

Do any of you know of a method to add unique features to an attribute table? I'm thinking that I can compare the original table to the "cleaned" one and add the missing points back.

Thank you so much!

  • In ArcMap are you deleting solely on the Shape field? – Paul Aug 15 '13 at 15:56
  • I'm using the Lat/Long fields. – Ross Wardrup Aug 15 '13 at 15:59
  • You should try with the Shape field. It should be more exact and is guaranteed to be up-to-date. – Paul Aug 15 '13 at 16:00
  • You might see if the ArcGIS Select by Location tool selects points that are in your original dataset but not in the one with deleted points. If so they could be added to the latter in an edit session. I've found I often need to use a very small buffer to catch all the identical. points. – johns Aug 15 '13 at 20:30
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Since you are dealing with coordinates that are the same, Near (Analysis) will do the trick. Use a very small search radius such as 1 foot or one meter. Points that have a value greater than -1 in the newly added Near_FID column are duplicates.

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Paul had it. Turns out that the geocoding software we use (MapMarker) threw a lot of the points into zip code centroids, giving them the same coordinates. I had to go in and look at the scare that MapMarker gives the points and run "delete identical" only on exact matches. Now I get to manually geocode ~250 points. Fun week ahead.

THanks everyone!

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You might try this: If your attribute table already has x,y fields (if not, then create two new fields to hold the x,y values and calculate the geometry to get the coordinates) then create a new string field and calculate the x,y's into the new field (field calculator > expression: [X] & " , " & [Y]). Once this is done you can use the summary statistics tool against the new field and use "count" for the statistic type. This will return a table showing which x,y combinations have exact duplicates (the "count" field will show them with a number greater than 1). Since I don't know how many records you have in your file this next part may or may not work for you: You could add a field called "duplicates" to you summary table and then select all of the records with a value > 1 and calculate the records to "yes". Then switch the selection and calculate the rest of the records to "no". Then set up a one-to-many relate between your points and the summary table, select the records with "duplicates = 'yes'" and deselect the records you want to keep and then delete the rest. This may be too cumbersome for your purpose but maybe it will point you in the right direction. Good luck.

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http://www.gpsbabel.org/ GPS babel has many options to help you manage point data based on attributes, distance, etc

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