Thursday, July 11, 2013

Viewing Chelan County land from the air using ARC GIS and Google Earth

There are free ways to display a bird's-eye view of your forest, if you're willing to put the time into it.

We bought our property many years before there was Google Earth. Microsoft had a demonstration web site called Terraserver (which still exists today as a separate entity) with satellite photos of Earth, but the resolution was inadequate. I hired a pilot to fly me over our  canyon so I could take my own photos. That was then.

Today high-resolution aerial photos are in the public domain and we can browse them on Google Earth. It's still no easy matter to locate the boundaries of a property relative to landmarks visible from above. There are dense trees over here, but are they yours?

Google Earth displays aerial photos but it provides
no information about property boundaries in Chelan County WA.

As of this writing it's still not possible to locate a Chelan County WA Assessor's Parcel in Google Earth Pro, nor to display the US Parcel Data Layers for this area. (It is available in other areas. You can get a free 7-day trial of Google Earth Pro -- before you buy it for $399 -- to find out if this area has been added.)

The county tax assessor's web site has a parcel search from which you can link to vector maps of parcels without aerial imagery. It's a conceptual map whose primary value is to look up data about neighboring parcels. No vegetation, buildings or minor roads are shown.

Chelan County Assessor's web site has a
 basic parcel-mapping function.

Aerial images are available in the separate ARC GIS section of the assessor's web site. The application is slow and buggy but it does the job once you learn your way around in it. You search by your parcel number, then right-click the result and choose "Zoom To." Once zoomed in, check the box at left labeled "Chelan County Imagery -2006."

Chelan County's ARC GIS system displays
parcel maps combined with aerial images.

This way you can see whether a drainage or potential road location is on your property. (The drawn parcel boundaries aren't as accurate as an on-the-ground survey, but this method is far cheaper.) Unfortunately, the images from 2006 aren't current enough to monitor forest health.

To detect damage or infestations you'll need to fly over the property yourself. It cost me about $150 when I did it ten years ago. If you do this, I recommend first laying out some 8'x10' white or silver tarps at your property corners.

With the declining cost of drones and digital cameras, you'll soon be able to hire someone to fly a camera over your forest, photograph your trees and compile a composite image with accurately geo-referenced boundaries. Until then, you can accomplish a lot by learning to use the free tools available online.

1 comment:

  1. UPDATE: The GIS web site has been upgraded to new software since this writing. I'll leave it to you to figure out the search function. Once you've zoomed in on your parcel, click the "Layers available" at top and choose the last one, "2006 imagery" and wait for the aerial overlay to load.


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