How do you think about acquiring raster data?

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10-07-2015 06:30 AM
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New Contributor III

I'm looking to understand how experts may begin thinking about raster data acquisition for trail maps. Basically, where do you get your orthophotos for local use.

I'd like to build trail maps that include all the elements of a good trail map - routes, legend, compass, elevation change, and scale. I prefer to build them on ArcGIS 10.3 instead of ArcGIS online for practical purposes. I understand the data we need to be raster data, boundary lines, and gps data. Esri can help build the rest. I plan to use gps data that local trail users have created, ArcGIS 10.3 functions, and topographic raster data.

One thing I have learned is data can have a high monetary and disc space cost. That being said there are often free data sources, such as clearing houses, government sites, and third party sites. How do you navigate the network of sources? Or how does one, when tackling a project that requires raster data acquisition, start to think about getting their hand on useful raster data for ArcGIS use?

12 Replies
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MVP Regular Contributor

If you're doing trail maps, you'll probably need high resolution imagery, correct?

LANDSAT/ MODIS has free imagery, but it's not high resolution (~15M)

To start, do you need the imagery to be free?

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New Contributor III

Hey Mitch Holley, yes given that our budget is zero dollars absolute, we must use free data.

We plan to print the maps on regular paper for personal on the trail. As I'm pretty new to the ArcGIS platform (but learning!), I'm uncertain of the resolution we need (I would guess we want high res). Perhaps you could offer a brief overview of what, "it's not high resolution (~15M)"? What does the 15M mean? 

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MVP Regular Contributor
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MVP Regular Contributor
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MVP Frequent Contributor

If your project location is in the Western United States, a good free aerial imagery source is the National Agricultural Imagery Program (NAIP).  Most of their imagery is 1 meter resolution.  Note that the imagery is free for download; however, if you need a them to send you a copy on a disk then it costs money.

Downloads

https://gdg.sc.egov.usda.gov/GDGOrder.aspx?order=QuickState

Web Service

http://www.fsa.usda.gov/Assets/USDA-FSA-Public/usdafiles/APFO/2013_apfo_web_service_931.pdf

Chris Donohue, GISP

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New Contributor III

Wow that's great to know the NAIP offers 1 meter resolution imagery for free. Unfortunately though, we're located in Upstate New York, so they might not have imagery for out area. I'll check out their data to see if they have what we're looking for.

Also, I'll add this to my list of sites to use for sourcing raster data. Thank you! Great help!

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MVP Frequent Contributor

Actually, they do have all of New York - I was just looking at their datasets.  This surprised me, as they have traditionally offered datasets only in the Western US.  Times change.....

To answer your question to Mitch, "15M" is shorthand in the imagery world for 15 meter resolution.  In other words, each "cell" you see on the image is 15 meters across.  By today's standards that is somewhat coarse, though still suitable for some uses.  For what you are doing, though, 1 meter resolution would be good (and even better resolution like 1 foot can be better, though their can be drawbacks like filesize).

Chris Donohue, GISP

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New Contributor III

Glad to hear that we're both learning Chris! Thanks for the explanation!

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MVP Frequent Contributor

Here's some more New York imagery:

NYS Interactive Mapping Gateway

NYS GIS Clearinghouse - Orthoimagery

Note that for many areas they also have several years of imagery available.

Also, another consideration for imagery is what time of year it was taken.  Depending upon what you are using the aerials for, you may want to get imagery from a certain time of year.  For example, if you want to see trails, getting a late fall image when the deciduous trees have lost their leaves ("leaf off") may help in seeing trails on the image.

Chris Donohue, GISP