Pavement Ends
Title

Unimproved Roads Near Clarksburg, CA: That Are Rideable Using Road Bikes!

Author

Glenn Chadwick
American River College, Geography 350: Data Acquisition in GIS; Spring 2009
1594 Caramay Way, Sacramento, CA, 916-662-3241, govt_scribe@comcast.net
Abstract

This paper evaluates the accuracy of GIS road map resources of Yolo County and ESRI that are available to the public for download. GPS waypoint and track data was captured using a Garmin eTrex LegendCx hand-held GPS device. GPS data was uploaded using DNR - Garmin software, post-processed to correct operator errors, and uploaded to ArcGIS 9.3. Resulting waypoint and track layers were compared to the Yolo County/ESRI base map to verify the accuracy of all acquired data.
Introduction

Bike racers living in South Sacramento often ride Sacramento Delta roads for training. There are numerous, small paved and unpaved roads along slough levees and farm boundaries that are passable using road bikes, but not all are mapped properly. On maps, smaller local roads often appear paved and are not. Similarly, if not mapped, they may be groomed, rideable gravel . . . and wonderfully serene and interesting.

This project focuses on mapping small local roads within twenty miles of Clarksburg, CA that can provide alternatives to heavily traveled highways. The audience is bicycle riders on road bikes with tires no wider than 25mm.

Shapefiles available for download from public agencies and ESRI are overlaid with a passable road layer. Passable roads are classified by type, with surface-level photographic evidence at road transitions.
Background

Bike route maps of Yolo County are ubiquitous and available online from numerous government agencies. The most prominent examples are produced by CalTrans and available on web sites like SacRegion511.org. There are also many cycling enthusiast self-generated maps posted online that leverage Google maps, like those at bikely.com.

The majority of these maps feature wide roads with plenty of vehicle traffic. I used them as a counterpoint to the roads I was looking for; if these maps overlooked certain roads, those were the roads I wanted to see!

Bikely
Methods

I acquired two road shapefiles and overlaid them to create a base map for taking GPS measurements in the field. I used the Add Data From Resource Center feature available from the ArcMAP File menu to acquire a general road map: ESRI's World Street Map. I also acquired a somewhat more reliable local road shapefile from Yolo County GIS web site called Road Center Line (which shows as purple line features below).
Base Map
Using Clarksburg as my base, I drove each road looking for unmapped, intersecting smaller roads and changes in pavement from asphalt to gravel. At each observed pavement/dirt transition, I: (1) marked a waypoint, (2) took a photo of my GPS device showing coordinates, and (3) took photos of the road surface and road signs or other discernable markers.
Waypoint Road Surface Marker Road Sign
I also recorded a track as I drove each non-asphalt sector and noted the qualities of the surface, my classification scheme simple: nice, rough, forget it. (The Pumphouse Road track is shown below in orange).
Track
Results
Sub-meter accuracy was not a necessary goal for this project, as bike riders merely need to identify roads, so most waypoint accuracy is within 10ft.

Track data is similarly accurate.

Figures and Maps
Below are general and detailed maps.

Final Map
 This is the final map showing unimproved roads with a classification scheme:
yellow = nice
orange = rough
red = forget about it.
Rose Rd
 I verified that the Yolo County Center Line Road shapefile accurately shows the location of Rose Road.

It is not paved.
Are you sure?
 I identified an area with a likely unmapped road . . .
Yes!
 . . . and verified there is a road there. It is on the Yolo/Solano county border and I suspect neither county wants to claim it.
Analysis
As a novice, my lack of familiarity with my GPS device and inexperience collecting data proved troublesome. I was able to successfully mark waypoints and tracks, but did so using an incorrect datum and did not stop/start the first few tracks properly. Re-acquiring the data was not a possibility, so I was forced to work with what I had.

Fortunately, the waypoint coordinates could be projected in ArcMAP and proved accurate enough for map creation.

Separate track data was initially appended by the GPS device to a single file due to operator error. It was necessary to edit the single track file into separate track files to eliminate appended data rows. This solution was time-consuming, but effective. After manually editing the track files using DNR-Garmin, the could be saved as unprojected shapefiles and used for map creation.

Conclusions
This mapping project identified what is there. Additional work could be done to debunk the ESRI World Street Map, which shows numerous roads that are in fact driveways, tractor paths through private farms, and gated levee slough roads clearly marked with no trespassing signs.