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I am looking for a coordinate system of New Zealand. I just have x/y coordinates of the south island, but no further information on the map. I have tried several systems and nothing did fit the data points.

A scatter plot of the points has shown that the points are even mirrored. The values do look like below.

7340311 46446451
9176667 45905000
7379577 46435685
7373889 46465000
7410593 46700702
10273967 43753542
7419167 46463056
7419787 46703207
6768776 48687156
9497410 44102852
8673500 47756069
6754167 48717222
8255278 46105833
6781457 48672920
6715970 48729233
10603611 44749722

example

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    I played around with them a bit. I think the points are in decimeters or centimeters or decimal yards (I tried the older NZ South Island grid). Adding a decimal point either one or 2 places from the right resizes the data so that it will fit on the island at least. I still couldn't make them work even with using the numbers as northing,easting.
    – mkennedy
    Commented Jun 24, 2019 at 21:29
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    Would help if you included the coordinates as text rather than an image, then we don't all have to type it in with all the problems that might occur.
    – Spacedman
    Commented Jun 24, 2019 at 21:54
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    Which projections have you tried already, and do you know which is easting and which is northing?
    – alphabetasoup
    Commented Jun 24, 2019 at 22:49
  • I tried several UTM like 1S, 2S, 59S and the 60S. I also tried the New Zealand Transverse Mercerator (NZTM) and other coordinate systems, proposed by this page: apps.linz.govt.nz/coordinate-conversion. I also georefernced a NZ South Island Map on this unknown coordinate system and I could provide some NZTM or World Geodatic System approximations, if this would help. I have no further information, neither easting or northing, nor meta data. I have attached the picture of the scatter plot
    – ulicious
    Commented Jun 24, 2019 at 22:56
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    Perhaps try Spatial Adjustment? In ArcMap, there is a Spatial Adjustment toolbar that allows you to specify links between your data points and their corresponding real location, then adjust the data itself. It's hard to tell which projection would be best, since we have no idea how these coordinates were created, but I would try with a transverse mercator, or maybe even plain WGS84 (4326).
    – FSimardGIS
    Commented Jun 25, 2019 at 1:19

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I finally found a solution to fix the issue.

  1. I have used a linear model in Excel, first, to convert the coordinates into the NZTM system. Here, I used Google Maps coordinate approximations of very noticeable points like crossroads etc as input.
  2. I plotted the calculated data with the new coordinates on a base map and used the spatial adjustment tool (rubbersheet), as suggested by @FSimardGIS, for the fine-tuning. The result is pretty accurate and I think close enough to further work with.

result

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  • And just to complete the answer: a friend of mine even cracked the code to transform it into WGS: x: 180 - x_location / 10^6 y: -90 + y_location / 10^6
    – ulicious
    Commented Jun 28, 2019 at 15:32

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