Creating fishnet based on DMS Coordinates

Question

I am trying to create a random sampling map of an ocean area. To do this, I would like to create cells that are 1' x 1' in size (one minute by one minute in DMS). My map is using WGS 1984 Web Mercator as the coordinate system. Whenever I go into the Fishnet tool, it asks for cell size, but this appears to be in meters.

One minute of latitude is supposedly 6,068 feet (1.15 miles) which is about 1849.526 m and one minute of longitude is 4,800 feet or about 1463.04 m.

The issue is that this projects a straight solid grid onto the map, which when I compare it to a graticule in the layout divided into 1' ticks, these boxes do not line up. I am completely okay with having not perfectly straight boxes as I am working with a large area and am expecting curvature.

The graticule would be fine to use as a grid system but I will later be stratifying the map and need to export cell data, which is why I am trying to use Fishnet.

Answer 1

I drawn big rectangle in DMS system:

and computed small squares (see script) inside it:

W,H = 0.016666666666666666,0.016666666666666666

and this is zoom to one of the pages:

Script:

import numpy as np
inExtent = arcpy.GetParameterAsText(0)
outPages = 'in_memory/pgons'
W,H = 0.016666666666666666,0.016666666666666666
arcpy.management.CopyFeatures(inExtent, outPages) #precaution if extent is wrong
## fishnet parameters
d = arcpy.Describe(outPages)
SR = d.spatialReference
ext = d.extent
toX,toY = ext.XMax,ext.YMax
x = np.arange(ext.XMin, toX, W, dtype=float)
y = np.arange(ext.YMin, toY, H, dtype=float)
fromX,fromY = x[-1]+ W, y[-1]+ H
mg = np.meshgrid(x, y)
X = np.array([0,0,W,W])
Y = np.array([0,H,H,0])
dX,dY = (fromX - toX)/2, (fromY - toY)/2
pgons = []
for x,y in np.nditer(mg):
    arr = arcpy.Array([arcpy.Point(x,y) for x,y in zip(X+x-dX,Y+y-dY)])
    pgons.append(arcpy.Polygon(arr,SR))
arcpy.CopyFeatures_management(pgons,'Feature calss of your choice')

I used script because I have it handy, but your can create XY to line tool to create set of vertical and horizontal lines (use Excel?) and make required size squares from them.

Note: Geodetic Densify tool made no visual difference at page level.