How to plot a contour USA map from a Shapefile

When I read my shapefile I get this attributes:

S = shaperead('nsrdb_9814_dni_ovit.shp', 'UseGeoCoords', true)  

S = 

      1716115×1 struct array with fields:

        Geometry
        BoundingBox
        Lon
        Lat
        DNI

Where Geometry is 'Polygon' and DNI is the Direct Normal Irradiance of solar radiation:

I need to plot a result like this (where DNI is the scale for the colormap):

I tried

geoshow(S)

But I have a problem: the structure S is too big for my PC with 16GB of ram (out of memory error) and I didn't see the final result (with smaller pieces of S I can't see if I am in the right direction).

The ultimate question: How can I control the DNI scale to get that result (with hot colormap).

PS. here is the file if you want to play with it: Direct Normal Irradiance

Thank you very much!