I work for Spatial Data and Mapping and deal with geocoding scanned maps quite often. Some of these maps are scanned, others (I never saw the equipment) photographed by cameras in some kind of dedicated room.
I am assuming that once the map is geocoded it will be released to be used by others? For such map to be useful you'll need to build a metadata record, with lineage not only for the historical map, but for the method of geocoding, including estimated accuracy. This is why outsourcing to 'anyone willing', unless well supervised, may not be the best option.
I use ArcScan for my geocoding. I use whatever other digital data can find as my reference, topo maps, satellite imagery, aerial photography. I make notes for each map, writing down what references I used, how many points I had to create, what kind of errors they brought with each algorithm and I also save the point file.
Be aware that old maps were not always drawn in proportion and geocoding may not always be possible. Projection, as someone mentioned, matters also, depending on the scale of the map.
It also depends on the purpose of the map. For example, when I georeference old hand drawn land unit map I use, as my reference, satellite imagery and concentrate on matching landscape features. If man-made features (tracks, buildings) are coming out of kilter, I don't care. But I'd point that out in my metadata. So ask yourself - what is the purpose of this map, what is it going to be used for, and by whom. Good luck!
Slashdot Mirror
Little Brother
I work for Spatial Data and Mapping and deal with geocoding scanned maps quite often. Some of these maps are scanned, others (I never saw the equipment) photographed by cameras in some kind of dedicated room. I am assuming that once the map is geocoded it will be released to be used by others? For such map to be useful you'll need to build a metadata record, with lineage not only for the historical map, but for the method of geocoding, including estimated accuracy. This is why outsourcing to 'anyone willing', unless well supervised, may not be the best option. I use ArcScan for my geocoding. I use whatever other digital data can find as my reference, topo maps, satellite imagery, aerial photography. I make notes for each map, writing down what references I used, how many points I had to create, what kind of errors they brought with each algorithm and I also save the point file. Be aware that old maps were not always drawn in proportion and geocoding may not always be possible. Projection, as someone mentioned, matters also, depending on the scale of the map. It also depends on the purpose of the map. For example, when I georeference old hand drawn land unit map I use, as my reference, satellite imagery and concentrate on matching landscape features. If man-made features (tracks, buildings) are coming out of kilter, I don't care. But I'd point that out in my metadata. So ask yourself - what is the purpose of this map, what is it going to be used for, and by whom. Good luck!