The auditor’s site is my friend: Delaware County Auditor.
See above photo for an example of this.
I don’t know what your county is like, but here in Delaware County, Ohio where we built, we can add “layers” to the aerial of any property on the auditor’s site that show its contours, floodplains, estimated soil types (I still STRONGLY recommend soil testing by a soil scientist before buying any rural lot—I personally would not buy any lot for building without understanding the soils) and more. Most of the counties in Central Ohio offer the same features on their auditors’ sites.

To explain the photo above… the purple lines all indicate a 2′ change in elevation. So where they are all close together in our woods, you can see that the elevation is changing very quickly. We have a ravine that basically cuts in two directions across our property (yellow outline). Which is awesome for us because the ravine is wooded and beautiful—and even though we’re building on the high side of the ravine, the woods still provide a shelter for us to the north. You can see the barn in the aerial… the house will be in the corner of the grassy area behind it, nestled into a nice little pocket with the ravine on two sides.
Here is why we are not building on the low side of the ravine:

All that blue is a floodplain for the Big Walnut Creek. Again, a screenshot from the Delaware County Auditor. Are they wrong about the floodplain? We have standing water in that lower field in the spring, fall, and winter seasons… so you tell me.
Why do we like this place even with the floodplain?
Because it’s gorgeous. And nature LOVES floodplains. Especially ours, because we have it enrolled in a conservation program which dictates that we cannot mow or farm it outside of their wildlife-friendly specifications.
All we need is a little home site and a paddock. We can get that on the high ground. The rest, we are happy to turn over to wildlife.
Did I know all this when we first acquired our place?
Yes, but not on walking-the-property-for-a-year terms. Not like I know it now. Frank did not know this place, either. I want to explain that I’m speaking in “I’s” more than anything as I write about contours and auditors’ sites because I’m the one who grew up out here in a family of Realtors who study all of the above and walk properties all the time. Frank has his own multiple talents in supply chain (which I cannot fathom), mechanical things (also which I cannot fathom or I would not have used the word “things”), and everything hands-on—whether fixing the chain saw to remove a tree or actually removing the tree. Or fixing our sink. Or his parents’ sink. Or my sister’s car. Or my parents’ rototiller. He’s my husband and hero, and I am not in any way diminishing his role in our home construction by talking about aerial views and walking the property without mentioning him. Many, many mentions of him are on the way in future posts on our building experience.
Plus he’s very handsome and has big muscles. Here he is:

And he never grew up with cattle or dreamed that he wanted them or any kind of farm life, and yet he just dove right in with more enthusiasm and dedication than I ever imagined. (Yes, we have cattle. They are Evangeline’s.) (Frank now says they’re his.)
Heart.
So I think that’s enough for now. If you’re thinking of buying a lot and want to build on it, please check out your auditor’s site and see if you can add “environmental” or “utility” layers or whatever they call them in your county. If anything at all.
Rely on Realtors who know rural lots and can refer custom builders, soil scientists, and so on—and also do your own research. It’s fun. And it helps you get intimate with your future homestead/farmstead/wilderness living adventure.
Know your place. Love your place.