Carquinez Strait Maps -- Large Scale - Terrain and Contour Lines
Scroll down for a description of the data used in this map, or click anywhere on the map to view an 8.5" x 11" scaled PDF.
This 1:20,000 scale map is a subset of the mapped extent of the project. This scale allows the contour lines and terrain features to be shown at the same time while still having the hard-copy output scaled to 8.5" x 11" paper.
Base Map
The base map is comprised of three layers that are derived from 1/3 arc-second Digital Elevation Models (DEMs) from the USGS seamless server. ESRI's 3D Analyst was used to generate slope and hillshade analyses with 3x vertical exaggeration. The DEM was stretched according to elevation and color coded. These images were then overlaid with varying values of transparency to arrive at the terrain features of the map.
Contour Lines
Ten meter interval contour lines were generated using 3D Analyst from 1/3 arc-second Digital Elevation Models (DEMs) from the USGS seamless server. The output contour line table was then processed with the field calculator using the following VB expression:
Abs (([Contour] / 50 - INT([Contour] / 50 )) * 10 = 0)
This VB expression adds a field to the contour table to hold the result of the field calculator expression. The general form of the statement is:
Abs (([Contour] / X - INT([Contour] / X )) * 10 = 0)
where X is the product of the contour interval and how many contour lines one wants between labeled (boss) contour lines (n). The result is either a 0 or 1 with a 1 representing every nth contour line.
After the new field was populated the symbology tab was used to create a new label class via an SQL query where the new label class contained the records where the new field was equal to 1. At this point one can individually label this class with the Contour field from the contour analysis to visually have contour lines with labels denoting elevation every nth contour line.
This process yielded a label class that represents every five contour lines given a ten meter contour interval. This label class was given a different symbology from the intermediate contour lines resulting in every fifth contour line being bolder and labeled with elevation.*
Mapping the Park Boundary and Walking Trails
The boundary lines for Benicia State Park were captured as GPS waypoints and georeferenced to the base maps. Park boundary waypoints not available by foot were derived from the map after proper georeferencing was confirmed. The boundary waypoints were then converted into a polygon to allow showing the park as an overlay. The two mapped trails shown were captured as GPS waypoints and converted to lines.
Annotation
The annotation is stored as georeferenced symbology in the same file-based database that the base maps, vector files, and elevation data are stored in. The geodatabase dataset for the annotation contains five data classes: Land Area, Transportation, Land Features, Municipalities, and Water Features.
Each annotation class was defined with a default font, font size, effects (bold, italic, halo, etc.) and modified per instance when needed.
* Method provided by Steve Nakazono, M.A., GIS Analyst - Chevron Energy.