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The Sunburned Surveyor

Things Learned - Data Collection Mission #2

I took a day off from work on Friday, April 2. I spent the day in the Red Hills on my second data collection mission. I had a number of goals for this data collection mission, but was only able to meet two (2) of these goals. I find I run out of strength before I run out of daylight. I didn't always have that problem.

The first goal I reached on this data collection mission was the mapping of some of the "forest" of the Red Hills. This forest is made up of scattered Gray Pines and a few Oaks.

The second goal I had was to classify some of the geography peculiar to the creeks of the Red Hills.

Here are some of the things I learned from this second data collection mission:

• Some features (for example: trees) can cluster within the “bubble” of precision for a waypoint collected with recreation grade GPS receivers like the Garmin Vista H, the receiver I am using. Depending on the site conditions, this bubble might be 30 or 40 feet in diameter. What are the implications of this equipment limitation when you are trying to map things at small scales? Do you represent multiple features at the same waypoint location, even though they aren’t exactly in the same spot? Do you attempt to set up some local measurement system (like a grid that can be used with a tape measure or an assumed coordinate system using a transit) and then reference that whole local measurement system with a waypoint? How else would you determine (possibly) important spatial qualities of the features you are mapping, like the spacing and clustering patterns of individual trees?



• How do you determine the mapping limits when you are locating fairly uniform features? (For example: How do I determine if I have already mapped a particular Gray Pine when I return for another data collection mission?) Will a list or exhibit showing the latitude and longitude of the features I already mapped get me close enough? Do I need to use some other method, like defining my mapping limits with other prominent topographic features? (For Example: I mapped all of the gray pines on the west slope of the ridge between the road and the creek.) How can I determine if features are being double counted between data collection missions?



• What are the advantages of a feature specific data collection form (on paper) when collecting a large number of features belonging to the same feature type or class? (For example: Gray Pines) Is this quicker and more efficient than using an audio recorder to record audio notes of feature attributes? Does it produce better quality data because it eliminates the possibility of forgotten attribute value observations? I imagine that might be a problem if you were using audio recordings to make attribute value observations on a feature type with a large number of features. (You have to remember that I am not using a data collector or other mapping hardware with the ability to use digital data collection forms, and it isn’t practical to pack around a laptop in this terrain.)



• I noted that observing a large number of features of the same feature type or class can reveal unexpected patterns in behavior, attribute values, or relationships with features of another type or class. (Example 1: Most Gray Pine trees in the Red Hills fork into two or more main trunks not far from the ground. Example 2: Most creeks in the Red Hills are already dry at higher elevations, but are fed by springs in their lower elevations.) How many features does one need to observe to “see” these patterns? How much does this feature count change between feature type or class? Is there a way to mimic my human observations of these patterns in a computer program that analyzes the attribute values of a set of features? Is there a name for this phenomenon of patterns about a feature class becoming visible as a large number of features are observed?

There were a few of other questions that came to my mind during the mapping of the trees during this data collection mission:

• What makes a forest a forest?


• How many trees do you need? How dense do these trees need to be?


• Do you need trees of several species to make a “forest”?


• How does the spacing of the trees in the Red Hills impact the wildlife there?
How do I practically measure tree height in the field, which is a lot harder than it sounds?

The Sunburned Surveyor

Introduction

As a land surveyor and a GIS programmer I have an interest in geography. I decided to start a small volunteer project to learn about the geography of the Red Hills, an Area of Critical Environmental Concern in Central California managed by the BLM. You can learn more about this volunteer geography project on the Red Hills Geography Project web page at the Redefined Horizons web site.

You can read this blog for updates on my progress with the project, to find out what things I am learning from the project, and to consider questions the project has raised in my mind about geography, surveying, programming, and other related topics.

The Sunburned Surveyor