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I have a data set of 3000 plots with coordinates in Lat/Long. It spans 13 UTM zones. I want to break it up into chunks corresponding with the 13 UTM zones, and convert the coordinates in each chunk to their appropriate UTMs.

How would I figure out which UTM zone each coordinate should be in? I would prefer to use R, but could use QGIS if necessary

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UTM zones are 6 degree bands, see figure https://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system - and then the EPSG code is 32600+x where x is the band number. e.g. New York is between 72W and 78W so that's zone 18, North, so use EPSG code 32618: https://epsg.io/32618

There are some exceptions where UTM zones get split and tweaked in various places but the outline above should suffice for most things.

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  • don't south zones have a different starting number? – Ian Turton Apr 30 at 7:23
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    Oopsie. Yes, southern zones appear to be 32700+zone number. epsg.io/32718 - although the only difference is the offset, so its okay to use N zones for data in S and vice versa as long as you use the right code. – Spacedman Apr 30 at 8:40
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There are also some on-line converters to do both-way transformations. This one permits batch conversion of data from a csv file:http://www.earthpoint.us/BatchConvert.aspx Though you do need a subscription for batch processing. I'm guessing there are others available that are free. One here, for example, though I haven't tried it.https://consult.hermes.com.np/batch-convert-lat-long-to-utm/ See also other question/answers like this one: Convert Lat/Long to UTM

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The QGIS Custom Expressions tutorial gives a function that will return the UTM zone (for most zones) you could use that to add a new (virtual) attribute to your data and then do a reprojection based on that value.

import math
from qgis.core import *
from qgis.gui import *

@qgsfunction(args=0, group='Custom', usesgeometry=True)
def GetUtmZone(value1, feature, parent):
    """Return the UTM Zone of the feature's geometry as a String"""
    centroid = feature.geometry()
    longitude = centroid.asPoint().x()
    latitude = centroid.asPoint().y()
    zone_number = math.floor(((longitude + 180) / 6) % 60) + 1

    if latitude >= 0:
        zone_letter = 'N'
    else:
        zone_letter = 'S'

    return '%d%s' % (int(zone_number), zone_letter)
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Another approach that was suggested to me on Reddit was to use a spatial join with this shapefile: https://hub.arcgis.com/datasets/esri::world-utm-grid/data

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