Consistent Square Grids -- "Make Grid" tool only just kind of working...

Question

Hello Alteryx Community! Long time viewer first time poster.

I am trying to create a single point layer (plots), spaced 600 feet apart overlayed across a 5 state footprint in the south/central US. The overall method I am using is working directionally well. However, when I measure distance between points I get  measures of distance between points that don't equal the parameter's I set up in the Make Grid tool

Currently I use the Make Grid tool, set the grid length to 0.18288 km (600 feet). Then I use the Spatial Info tool to derive the centroid of each Grid cell to create the point layer. Theoretically the centroids should remain 600 feet apart across the 5 state footprint. But that is not the case.

The attached image shows that the distance West to East between points turns out to be 601.59 feet, and the North to South Distance is 598.85 feet. While this is directionally accurate, I need precise distances as our methodology is heavily critiqued.

I have played with using the Grid endpoints (via spatial info tool) to then select either the First or Last point of the grid, rather then the grid centroid, and the issue remains the same.

How can I space these points exactly 600 feet apart? Is there a setting that will allow me to select distance in Feet rather than km or miles? Would I be better served to use another process? Can I adjust the distances between the spatial objects using a formula?

ALteryx Distance Grid.png

Create Grid workflow.png

Deanna · Accepted Answer

Hi, @WillWork4Trees and thank you, @MarqueeCrew for the introduction!  Glad to help; @WillWork4Trees , you are doing everything right in your process, such as creating the grid, using Spatial Info for the centroid, then calculating distance, etc.  It turns out that Alteryx actually uses a WGS84 coordinate system for all of their spatial processes, including creating grids and calculating distance.  This coordinate system is simply a "grid" across a perfect sphere, which makes it easy and fast to calculate distance - however, the Earth isn't a perfect sphere, instead it's a geoid, or "squished" sphere.  :)

This can result in slightly less than precise measurements in gridding and distance calculations, which is what you are finding. I have used Alteryx since 2005 for spatial analytics, and for the bulk of these analytics, it is just right - and super fast.  However, whenever more exact distance measurements are required, I usually recommend (especially to GIS professionals) to use a GIS platform such as ESRI ArcGIS along with the corresponding datum or projection.  Even then, if true precision is needed for legal requirements, I usually recommend using a survey team to accurately measure the distance on the ground.

There is a really good post in the Community about "How Does Alteryx Designer Handle Spatial Data?" which can be found here:  How does Alteryx Designer Handle Spatial Data?

The information about the WGS84 coordinate system is near the bottom of the post, and here is a copy to make it easier to find:

"All spatial data read into Alteryx is automatically transformed to a WGS84 datum with a latitude and longitude coordinate system.

Spatial calculations in Designer are performed on a sphere with a radius between the polar and equatorial radii of the Earth. This does result in some distortion in calculations. Near the equator, distance calculations can be 0.2% smaller than their actual size, and near the poles, distance calculations can be 0.2% larger. Within the US and Europe, distance calculations are more accurate. Alteryx does not use any projected coordinates when performing spatial calculations."

I hope this helps, and please feel free to reach out to me on the Community using @Deanna ; I have been performing GIS analyses for 25 years, and am always excited to assist others in exploring spatial analytics!

P. S.  GIS platforms such as ESRI ArcGIS can output shapefiles (.shp), which can be imported into Alteryx.  You can also output spatial object fields in Alteryx as .shp and then import them into a GIS as well!  The same goes for MapInfo .tab and other spatial formats.  Using Alteryx and a GIS together can potentially speed up quite a few processes and be very beneficial!