Spatial Interpolation of categorical vegetation data

[chrisstockdale]

I have built a vegetation map from a set of historical photographs from 1912. The photographs were taken from the ground (ridges and peaks of mountains), and I have developed a method of georeferencing these images and extracting gridded data of the vegetation types visible.

However, there are many portions that were not visible in this landscape due to being obscured behind ridges. These locations were not visible from other camera photo points. This is not a dissimilar problem to aerial photography with lots of obscuring clouds. The difference is there are not other photos to use to fill in the gaps. I need to use some sort of interpolation routine to fill the gaps.

I am currently using ArcGIS 10.2.2 and would like a solution that works within Arc, but if it is not possible, I will entertain using R or QGIS or other packages.

I need to interpolate the vegetation categories in the obscured areas. My hypothesis is that it is driven by aspect/slope/elevation and of course influenced by the nearby vegetation. I think this is some variant of co-kriging, but I have not been able to track anything down that deals simultaneously with categorical and polygon data. The data below in the image is in 100m square cells.

Does anyone have any suggestions of approaches to take? I would like to bootstrap the data so that I can test its predictive power, rather than just interpolate what is missing.

Attached is a map showing what I am dealing with. THe different colours indicate different vegetation categories (ie coniferous forest = dark green, deciduous = pale green, shrubs = orange, grassland = tan, open canopy forest = black). The grey areas are the obscured areas. Click on the attachment below to see the map

[ChrisDonohue__GISP]

A suggestion/possibly more picky than you need, but worth considering:

One other data source that can influence vegetation that you may want to check is soils/geology. As an extreme example, the presence of a Serpentine belt in your project area will totally alter the vegetation that can grow there (to the point that there are several species uniquely adapted to handle that environment).  If you have tilted strata, this will be independent of elevation and slope.  So if you have soils/geology available, I would check that.  The geology is not likely to have changed much since 1912.

Serpentine soil - Wikipedia, the free encyclopedia

Soils and Plant Adaptations

Chris Donohue, GISP

[chrisstockdale]

Unfortunately I do not have soils information for this area. There is a general soil map for Canada that would provide coverage, but this soil map is not sampled in the field to a resolution that is any use for this study. I am stuck with the few variables I describe above.

[DanPatterson_Retired]

Can you validate using current satellite imagery?  If the vegetation is mature, then this would be preferable to an extrapolation. Validating what you have now given your current data would allow you to propose what it might have looked like.  You mentioned Canada, the gov. released a whole slew of imagery last year rather than charging for it as was previously done.  You might want to try one of the sites, which I can't remember off hand (GeoGratis?? or its ilk)