How to transpose reclassified field values from one polygon shapefile to identical polygons of another shapefile?

Question

I used vector output from modeling software as clip features for ecoregion input. I reclassified and dissolved the clipped layers into 3 subunits, and now would like to transpose those simplified values to the source ecoregion layer in areas of intersection, such that the same 3 field values from the clipped layers are mapped onto the source ecoregion layer.

I need to do this for about 200 pairs of shapefiles, and it seems like there must be some at least partially automated way to approach this.

In the image below, I've symbolized the 3 field values semi-transparently over the source ecoregion layer. You can see that a single value polygon in the top layer overlaps multiple polygons in the source layer, but the outer boundaries of the individual polygons of the source layer exactly match the simplified polygons of the top layer.

In this image, I've reclassified the source ecoregion layer to match the field values of the top layer, such that the field values from any polygons from the top layer that intersect with polygons in the source layer are copied to the attribute table of the source layer.

I've been doing this via manual selection and the attribute table field calculator, but this will take forever for 200 sets of vector data.

Anyone know of either a canned tool in arcGIS that could help with this, or python coding approach that could help speed this up?

Thanks in advance for your help!

EDIT in hopes of clarifying: For polygons in the reclassified Layer A and Layer B (ecoregions) that intersect, I'd like to populate the subunit field in Layer B with the same value as the subunit field in layer A.

This is the attribute table of the reclassified Layer A:

This is the attribute table of the source ecoregion Layer B after I've manually populated the subunit fields based on intersection with Layer A:

Answer 1

The type of relationship between your two levels of polygons is not perfectly clear, but I think that you could do this in a few automated step in any cases.

Case 1 : Many to one relationship. In other word, the smallest polygons are never overlapped by more than one type of the larger polygons.

In this case, you can use "intersect" or "spatial join" that will create a new feature class where you will find the attributes of both layers. If, for some reason, you do not want to create a new feature class, you can also build the centroids of the small polygons (feature to point with the INSIDE option, spatial join with the large polygons, the table join to have the attribute in the attribute table of the small polygons).

Case 2 : Many to many relationship. In other words, one small polygons could overlap two or more regions. Then you need to concatenate the field information.

This case is more complex. You can first run "Tabulate Intersection" in order to have a table with all the overlap. You can directly create a relationship between this table and your small polygons, but this might not be exactly what you are looking for (you can see the information with the identify tool, but many tools will not be able to use a relationship directly). If you are sure that there is never more than two overlapping features (this is likely to be the case from what I see on your illustration), you can then use "summarize table" on the OID of the small polygons with first and last values of your field of the large polygons. Then you have one table with the OID of your small polygon, the first value of your larger polygon and the last value of the larger polygon. based on the field calculator, you can concatenate these values.

code block (Python)

def concat(first, last):
    if first == last:
        return first
    else:
        return (first + " / " + last)

in the calculator

concat(!first!, !last!)