Coastline extraction from historic maps

Question

Hi-

I'm trying to extract the coastline from a series of historic (hand drawn!) maps (I got the idea from NOAA). The maps are all scanned, rasterized (.tif files), georeferenced and correctly projected (NAD 1983), but I'm not sure what to do next!

Essentially all I want from the maps is the division between land and water, I can discard all other information. I was thinking I'd begin with a classification, but that's just a guess and I don't even know if it will work with these sorts of files. I also saw something about an indicator raster. Any and all advice would be appreciated! Thanks.

Emma

TrishRice · Answer

How many maps do you have?  Do you want to sketch them in by hand (using the Editor tools) or automatically (with Raster tools)?

The first thing that pops to mind is similar to Richard's comment about upping the contrast.  Doing Reclassify would allow the boundary line to become more distinct.  Then some of the raster to vector tools may be helpful.  Have you asked over in Imagery & Raster Data?

RichardFairhurst · Answer

Hi-

I'm trying to extract the coastline from a series of historic (hand drawn!) maps (I got the idea from NOAA). The maps are all scanned, rasterized (.tif files), georeferenced and correctly projected (NAD 1983), but I'm not sure what to do next!

Essentially all I want from the maps is the division between land and water, I can discard all other information. I was thinking I'd begin with a classification, but that's just a guess and I don't even know if it will work with these sorts of files. I also saw something about an indicator raster. Any and all advice would be appreciated! Thanks.

Emma

I am not an expert in using the raster options of ArcMap, and more than likely that will be your best option, but I will let someone else with more experience describe how to use those techniques.

However, if the boundaries of the two areas are distinctly drawn, either with a fairly think boundary when there are no fills or with solid fills of obviously different grey scale values on each side of a boundary, I have used photoshop to convert the image to grey scale, enhance the contrast, and do a trace using their trace tools.  The vectors created by the trace were saved from Photoshop to a supported CAD format that ArcMap could open.  The CAD file was brought in, georeferenced and converted to a line feature class with the CAD conversion tools.  I think that before I did the trace I first used the georeferencing tools to match up the image to my map, and actually did the trace on an exported georeferenced image from ArcMap rather than the original image itself.

The conversion won't be perfect and some clean up to remove traced text objects and unwanted scanning artifacts will be needed, but it worked fairly well for me when I was converting scans of Specific Plan land use plans that depicted land use planning area boundaries.  I had to play around with the Photoshop trace tool settings and this technique is highly dependent on the quality of your originally scanned image (but probably most techniques are heavily affected by that, whichever way you go).  Most of the work was in deleting the traced text objects and doing a few line extensions to connect the boundaries where text got in the way.  Then the line set was converted to polygons and those polygons were checked again for correct boundaries.  Final clean up was done with the Split Polygon edit tools in a few cases.

I'll be interested to hear about any workflows that relied on Arcmap's built in raster tools myself, but I hope this helps and provides an option that may work with your image.