I don't know man. If steam junk -- whoops, I meant steam punk -- can be cool, analog imaging can be cool again too, eventually.

Useful? A good question. At some point, you will run up against a limit caused by the quality of the old mapping. The old one you chose is one of the best years. We have seen accuracy decline in the editions following.

It seems to me USGS ought have a reliable method to adjust for that datum change.

D 2

I find your new historical maps page spectacular and most useful. Its difficult to usefully combine map layers (essentially different maps with different information) without it getting cluttered but that slider makes it easy. I checked out a couple of areas I am familiar with and was able to see where trails once went that I haven't been able to locate. I have access to the maps you use but its much more difficult to compare two separate maps in comparison to your online system.

Good luck on adjusting between the various mapping systems. Their is no easy fix as the WGS-84 introduced time as a factor in mapping which is meaningless in the older systems used in virtually all our maps.

The USGS is using NGVD-29 including for our local river gages and most maps, while FEMA and the Army Corps of Engineers uses NAVD-88. The two systems have different opinions of what sea level is, with the earlier NGVD-29 system placing it 3.49 feet lower than the newer NAVD-88 setup. With the rise of sea level the higher figure is better! An earlier system still seen on older maps had sea level 8.1 feet lower.

Originally all mapping was done by physical measurements using chains 66 feet long with one inch links. Everything referred back to a starting point, which in our area is the Willamette Stone, located in a state park in Portland's West Hills not far north of Burnside. This system gradually modernized with the final attempt adding reference to an idealized center of the Earth. The more modern WGS-84 does this also but unfortunately with better science and more precise equipment it was decided the center of the Earth was really a few feet over from where the last NAD system placed it. Reading the pdf at www.naref.org/transf/nad83_hydroscan2006.pdf‎ you can find the statement that between the systems the error in parts of Canada is 1.5 meters horizontally and .2 to 1 meters vertically. These errors vary from place to place. There is also an interesting map graphing these shifts for many spots in Canada. If the pattern shown in Canada holds into Oregon, new WGS based maps will shift everything near to east about 5 feet. Everything refers to the Earth's center so coordinates shift with the motions of plate tectonics over time. Coordinates given with the WGS system are fully accurate only for the given date.

The older systems will continue to be used for mapping as long as it is easier and cheaper than converting many years of systems, data and map making to the newer system.

From the Canadian document: "Although the national geodetic agencies in both Canada and the U.S. adopted a common transformation between NAD83 and the various ITRFs for use with the new realizations of WGS84, the bias between NAD83 and WGS84 was never acknowledged by the agency maintaining WGS84. Consequently, the vast majority of GPS receiver manufactures continue to treat NAD83 as being identical with the new realizations of WGS84 which results in position errors of over a meter. Moreover, ITRF-based systems are global systems in which all the continents are in continuous motion due to the Earth’s tectonic forces while NAD83 is fixed to the North American tectonic plate and move with it. Consequently, NAD83 moves at about 2.5 cm/y relative to the ITRF/WGS84 systems."

BTW, 2.54 cm is an inch. So 12 years is a foot of error, 36 a yard. Makes you glad you'll only live long enough to see around 7 feet of this go by.

Many of the errors mentioned in the comments here are likely a result of inaccurate surveying. Any inaccuracy over a couple of yards isn't likely to be from the newer mapping system.

I would not be surprised if the phrase "Good enough for Government work" was first uttered by contractors dragging a 66 ft. chain and transits up near vertical Cascade Mountain slopes quickly enough to fulfill the terms of their government contracts. And it sounds like its still being said in certain agencies.

Bryon

Thanks, Bryon.  I thought I had corrected for the datum (or at least close enough), by using a tool like this that Paul had referred me to:

http://www.ngs.noaa.gov/cgi-bin/nadcon.prl

It shows the shift as about 95 meters.  When I use the adjusted coordinates it still isn't quite right - part of that might be that I'm using a really old version of some mapping software (global mapper) that might just be out of date.  Commercial GIS software is horribly expensive, and the open source stuff I just don't understand.  Trying to do this with a very limited knowledge of the space is hard.  I just wish more of this made sense.

I did find out that under NAD27 (what most of these maps were created with) that it is very North American centric.  Apparently there was some "ranch" somewhere that was the center of the country, and everything was in relation to that point.  That worked OK for North American maps, but when trying to map the world, it failed, so they came up with NAD83 and WGS84, which, to my limited mind is basically just a mathematical model for translating a spherical object (the earth) onto a flat space (a map).  If I could get the maps down to a 1 meter or even 5 or 10 meter variance, I'd be happy, but I'm not there yet, so I keep experimenting.

The next iteration I will have the ability to select which overlay you want.  So, you can select the basemap (current map) and also an overlay choice.  I'm still working on it, but it is coming along.

Donovan, you must have been down at the steam-up last weekend!  We are probably going to go next weekend, as my father-in-law has a tractor displayed there.  It is always a fascinating day.

Back to working on the maps....

Would there be a way to click on and drag the overlay once we were on a focused area to line up known features?

D 2

Donovan said
Would there be a way to click on and drag the overlay once we were on a focused area to line up known features?

Unfortunately, no-or at least not any way I'm aware of.  That is the whole purpose of having the maps georeferenced - they know where they are supposed to be positioned and everything is set upon that positioning.  You can do it in Google Earth by adding an image overlay, but that is REALLY hard to do correctly.  It doesn't start with it "close" and you tweak it, you have to size the image perfectly to match the zoom level you have set, and then match up the image to the underlying map.  It is very tedious.