Surveying a home’s floor elevation and surrounding elevation points relative to a datum (i.e. Mean Sea Level) is not as simple as getting a region-based Topographic Map and basing your home’s floor elevation based on that, let alone getting an Altimeter to get a reading for you. The accuracy is questionable and at best will only give you an approximate elevation relative to mean sea level.
Elevations are simply an expression of the vertical relationship between points on the Earth’s surface. What is important to understand about elevations is that one must know on what datum they are based in order to use them properly. – Curt Sumner
Your best bet…
Your best bet is to leave it to the pros. Hire a surveyor and they can get all the elevations you’ll ever need to the decimal point! This could cost anywhere from a few hundred to a few thousand dollars depending on where you live and the complexity of the terrain.
Doing it yourself…
Not your best bet and could cost you a lot of time and the margin of error is much greater. BUT if you insist and if high accuracy was not critical, you could locate a benchmark and attempt to get your elevation points yourself.
The way surveyors do it is to go to a USGS “Benchmark”. It is a brass plate set in concrete at ground level that tells the elevation at that particular point. From there, they shoot elevations to the subject site. – Anonymous
Finding your Benchmark
An idea would be to talk to your neighbor and look for any plans that may contain a topography survey of the property and you can base your numbers relative to theirs.
If you’re up to the task, you could find your own benchmarks with the help of tools offered in sites like www.geocaching.com and www.ngs.noaa.gov. You’ll soon discover that Benchmarks aren’t always going to be conveniently located on the sidewalk in front of your house- this would be a miracle and you’ll now begin to see the value of getting a surveyor.
Alternatives to USGS “Benchmarks”
These alternatives are not to be considered accurate but perhaps useful to establish a placeholder baseline until you can get a surveyor to verify the numbers for you.
Based on Google Maps Services you could use Free Map Tools or based on GPS you could use Longitude Store. I prefer the latter because they give you a decimal value – however, you need to remember that the accuracy of these numbers are still questionable and should only be used to give you a rough estimate for your datum.
After finding your Benchmark…
Once a Datum is established, you could measure rises with the help of laser levels good old tape measure. If you wanted to step up your game and could afford it, a ZIPLEVEL PRO-2000B High Precision Altimeter will make grabbing those elevation point differences much easier.
There are no absolutes in surveying measurement. There will always be some amount of error. Controlling that error to be within acceptable standards is the objective. – Curt Sumner
Conclusion
Depending on your needs and circumstances of the home in question. Hiring a surveyor to establish your home’s elevation from mean sea level is not only practical but much more accurate. If you only need elevation points from a datum such as a sidewalk or a curb then you could do it yourself using a tape measure and laser or a high precision altimeter mentioned earlier.
Sources
-
How Elevation is Determined ( A great read!)
- Land Surveying and Conventional Techniques for Measuring Positions on the Earth’s Surface (How it’s done professionally)
- Help Determining Elevation! (good discussion)