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I've been trying to solve a problem for the last few days but not having much luck. I'm hoping someone here can point me in the right direction. I'm new to ArcGIS so I hope my explanation makes sense.

Here's my problem. I have a layer of points with x,y co-ordinates. They are laid out in a mecrator projection. What I need to do is create another layer with a grid. Each grid cell needs to be 2 degrees high, by 2 degrees wide, with the point acting as a centroid (so the boundaries are at a distance of 1 degree above the point, 1 degree below, 1 degree left and 1 degree right of the point). The grid cells cannot overlap. Because of the mecrator projection, I would expect the height of each cell (latitude) to remain the same, but the width (longitude) to expand the further away from the equator they are.

I've tried the thiessen polygon tool, creating buffers, the fishnet, and the minimum bounding geometry tool but its not quite what I'm after.

Any ideas? Any help is greatly appreciated!

Thanks very much

PS: I've popped a (badly drawn) image up on to G+ of what I want. See here. Figure 1 is what I have, and Figure 2 is what i need to create

enter image description here

Sam
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  • Your expectation is curious: because the cells are specified in terms of degrees, and because the Mercator projection is cylindrical, then necessarily (1) all cells will have identical widths (2 degrees of longitude) but (2) their heights must vary with latitude. In the Mercator projection the extreme example occurs for points near 89 degrees latitude: their cells extend almost infinitely far from the map's center, but still have widths of just 2 degrees. Nevertheless, in any (pseudo-)cylindrical projection all those cells will be mapped to perfect rectangles. – whuber May 19 '13 at 15:15
  • Try the method outlined here: https://gis.stackexchange.com/questions/29337/creating-square-buffer-around-point-feature-using-arcgis-for-desktop – spartmar Apr 26 '17 at 18:25

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These are the steps that I would use:

  1. Create Fishnet to create a 2 x 2 grid
  2. Define Projection on your fishnet as a Geographic Coordinate System (in lat/long)
  3. Project your GCS fishnet into Transverse Mercator

You should now see the expected broadening of cells at the equator.

PolyGeo
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    I would also suggesting Densifying your 2 x 2 grid since the actual resultant polygons will not be a true representation of the grid cell once projected. They will be flat in the East West direction rather than having the appropriate curvature which would be expected when following a parallel. See http://resources.arcgis.com/gallery/file/geoprocessing/details?entryID=C466543F-1422-2418-8843-D333B3EB1879 and experiment with various densifications (eg start with a 0.1 or 0.2 degree densification) –  May 19 '13 at 12:24
  • Definitely use ArcGIS Densify tool if you have access to Standard or Advanced license level. Or @DanPatterson Densify tool that looks like it may be designed for Basic too. – PolyGeo May 19 '13 at 12:36
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    Yes PolyGeo, originally this designed to run in 10.0 ArcView and it should run at all license levels in 10.0 and 10.1. It also allows you to produce a point file showing the locations of the densified points if they are needed for other analyses. –  May 19 '13 at 13:00
  • @Dan Patterson Concerning the need for densification, please see my comment to the original question. The four corner points will suffice to define these cells perfectly in either a GCS or in the Mercator projection. – whuber May 19 '13 at 15:17
  • Whuber, Perhaps I was thinking of what happens when using a UTM projection, then trying to perform a select by location (within) which produces erroneous results if the selection grids are not densified prior to projection. –  May 19 '13 at 18:06
  • Thanks for all the comments guys. I've had a go with the suggestions & it hasn't produced quite what I'm after-probably because I haven't explained what I'm after very well, & because I don't quite understand the system (but we have to start somewhere I guess). I think what I am after is something more like what the buffer tool creates...a polygon around each point (which lies at the centre), only square. Once its finished creating the buffer, I'll try the minimum bounding geometry tool to create the square. I'm hoping the results will work now I have corrected for the projection. – Sam May 19 '13 at 19:57
  • I've not been able to reach your link to see your two figures so I'll upvote your question to see if that may give you enough rep to include them instead. – PolyGeo May 19 '13 at 20:02
  • Thanks PolyGeo - that worked great. The picture isn't the best...it may not help – Sam May 19 '13 at 20:41
  • I think this can be done using not much more than Create Fishnet, Define Projection and Project but only if the points are generated and not provided - is that the case? – PolyGeo May 19 '13 at 21:46
  • Ah - the points are provided.... – Sam May 20 '13 at 11:56
  • It seems odd to me that they can be provided 2 degrees apart in X and Y if not generated. – PolyGeo May 20 '13 at 12:23