Training sample assignment of raster pixels to class

JanniceBanks — Wed, 03 Jun 2026 03:52:26 GMT

When training samples are developed for raster classification (using irregular polygons to manually perform a supervised classification), how is class membership assigned to the raster pixels for training? I think it's one of the following ways:

pixel membership to a class is assigned when any pixel of a raster intersects in any way with the training sample, OR
pixel membership to a class is assigned if the training sample intersects the input raster pixel centoid

The reason for my asking is that I’ve used python to developed a Withheld Data Test for my Random Forest/random trees classifier, which I’ve had to do manually.

The Withheld Data Test involves:

Create fishnet 1px x 1px
Intersect tool to select fishnet by attribute where it intersects with TS
Export selected pixels
Randomly assign pixels within the training samples fishnet a number 0.0 – 1.0, randomly split them 70%/30% and assign membership to two TS classes - Test30 and Training70. Note that these two classes maintain the class values of the original training samples.
Erase the location of Test30 pixels from the training samples, resulting in irregular polygons that look like Training70 fishnet.
The way I’m choosing the conditions of membership of the 30% of pixels that I’m excluding from my TS should be the same as how the training samples classify raster pixels into a class.

I hope that this makes sense! It would be great to get clarification so that I can tune my model properly. Also, this matters as the training samples I need to develop are quite small (i.e. IDing shadow for trees can be like 5x5 pixels, and for an entire site I’m often only training about 5000 pixels). It makes a big difference to my model (the 30% of test pixels can actually become 25 – 35% of the TS pixels if it's done inconsistently with how Esri does things). Thankfully, I'm getting 98% kappa value already, so the small sample sizing is working well.

Any help is greatly appreciated. \m/

Re: Training sample assignment of raster pixels to class

DanPatterson — Wed, 03 Jun 2026 13:06:25 GMT

Cell assignment depends on the geometry being converted. Discussions are in the following links

How Polygon To Raster works | ArcGIS Pro documentation

How Point to Raster works | ArcGIS Pro documentation

raster sampling by rasters would have to consider cell alignment and the snap raster

Cell Alignment | ArcGIS Pro documentation

Snap Raster | ArcGIS Pro documentation

so I would be concerned if the rasters are misaligned

topic Training sample assignment of raster pixels to class in ArcGIS Pro Questions

Training sample assignment of raster pixels to class

Re: Training sample assignment of raster pixels to class