This document discusses common pitfalls in geologic mapping and provides suggestions for a more efficient workflow. It outlines seven steps to avoid problems: 1) Have a plan for projections, scales, units and formats. 2) Organize data with descriptive naming. 3) Digitize as lines then convert to polygons. 4) Edit lines and attributes. 5) Maintain organization during edits. 6) Use standard symbology and attributes. 7) Write thorough metadata. Following a standardized, organized process from the start can help avoid issues like misaligned features, dangling nodes, and attribute errors.

1. GEOLOGIC MAPPING 101:
COMMON PITFALLS AND SUGGESTIONS
FOR A MORE EFFICIENT APPROACH
Mark Zellman1 & Kristi Zellman2
1Fugro Consultants, Inc.
2Colorado School of Mines and U.S. Geological Survey

2. INTRODUCTION

3. COMMON TASKS
Polygons
• Converting raster maps to vectors
• Scanned paper maps
• Digital raster images
• Cleaning up vector messes Vector Lines
• Symbolizing
• Attributing
• Metadata Raster Source
• Publishing

4. COMMON PROBLEMS: RASTER MAPS
• Missing spatial reference control
• Inaccurate spatial control
• No listed spatial reference information
• Obscure projections
• Shifted data
• Mapping errors
• Poor print quality
• Scanning of rare and brittle historic
maps
• Deep creases = warped scans

5. MORE PROBLEMS: VECTOR CHAOS
• Dangling nodes
• Polygon gaps or slivers
• Unclosed lines used to represent polygon features
• Duplicate lines for single contacts (polygon to line
conversion)
• Poor digitizing technique
• Disorganized data
• Feature alignment issues

6. MAP EXAMPLE

7. MAP EXAMPLE

8. MAP EXAMPLE
Unit overruns
Overshoot
fault contact
Gaps
Gaps
Map features
extend beyond Overshoot
boundary

9. UNCLOSED POLYLINES

10. MANAGING THE PROBLEMS
• Raster Issues
• Projections:
• Research (ASPRS is a good resource)
• Comparisons with satellite imagery, orthophotos, topographic maps
• Trial and error
• Warped Scans
• Georeferencing tools:
• 1st – 3rd order polynomial
• Stretch
• Vector Issues
• Data QA/QC
• Topology tools help!
• Educate misguided GIS users who pass their problems to you.

11. HOW TO AVOID THESE PITFALLS
• Learn how to use GIS tools effectively
• Don’t create GIS data in a graphics software package
• Understand your subject-matter to depict appropriately
• Use a standardized method for managing vector data
from the start…

12. STEP 1: HAVE A PLAN
• Know your:
• Projection
• Map scale
• Map units
• Establish a naming convention
• Organize the attribute table
• Consider the data format (shapefile or geodatabase)
• Not everybody can view your ArcGIS version 10 geodatabase files
• Vector structure (faults, contacts, folds, dikes, etc..)
• Plan the editing and revision process
• What about software??

13. STEP 1.1: SOFTWARE
• You’ve got options…
1. ArcGIS Desktop + Extensions
• Digitize shapefiles and convert to polygons with extensions (ET
Geowizards)
2. ArcINFO
• Create as shapefiles or geodatabase files and convert to polygons
• Create geodatabase files and establish topology then convert to
polygons

14. STEP 2: ORGANIZE YOUR DATA
• Develop an organized file structure
• Use a descriptive and progressive file naming convention

15. STEP 3: THE DIGITIZING WORKFLOW
• Digitize the units as LINES, not polygons
• If you were to draw units, how would you do it?
• Use the editing templates in ArcGIS version 10
• Digitize the map boundary and faults before contacts
• Keep cultural features, folds, hydrology separate – refer back to
your plan.
• Use snapping Points
• Save often!!!!
Separates
Geologic Lines
Geologic Polygons

16. STEP 4.1: LINES TO POLYGONS
• ArcGIS + ET GEOWIZARDS
Shapefile ET
Polygon v1
Lines v1 Geowizards
Build Polygon
Tool

17. STEP 4.2: LINES TO POLYGONS
• ArcINFO
Shapefile
ArcToolbox Polygon v1
Lines v1
Feature to
Polygon
Geodatabase Editor GDB
Lines v1 Toolbar Polygon v1
Construct
Topology Rules Polygons

18. STEP 5.1: THE EDITING PROCESS
• Maintain data organization and file naming conventions
• Develop an organized process for creating, editing and
updating files
• Edited polygons require updated attributes (preserve
attributes)

19. STEP 5.2: THE EDITING PROCESS
ArcToolbox
Points v1
Feature to Point
• Preserve Attributes
• Choose Inside
Option
Editor Toolbar Polygon v2
Option 1 Polygon v1
Topology Edits
ArcToolbox
Option 2 Lines v1 Line v2 Polygon v2
Line to Feature
• Import attributes
Edits from Points v1

20. STEP 6: SYMBOLOGY AND ATTRIBUTES
• Use standard colors for unit polygons and standard
symbols for geologic features (ESRI, USGS)
• FGDC Digital Cartographic Standard for Geologic Map
Symbolization (FGDC, 2006)
• ESRI Geologic Map Template
• ESRI symbol template pallet
• Important traits for attributes
• Consistency
• Limitation
• Descriptive
• Easy for a user to interpret

21. STEP 7: METADATA
• Take time to write thorough metadata
• Know what format your users are using
• Use a metadata editor
• ArcCatalog
• EPA Metadata Editor

22. CONCLUSION
• These approaches can be applied to projects in other
disciplines
• To avoid common mapping pitfalls:
• Take the time to make a plan before you start a GIS project
• Understand your subject matter and audience
• Always take the time to write thorough metadata
• A standard and organized approach is necessary

23. REFERENCES
Federal Geographic Data Committee [prepared for the Federal Geographic Data Committee by the U.S. Geological
Survey], 2006, FGDC Digital Cartographic Standard for Geologic Map Symbolization: Reston, Va., Federal Geographic Data
Committee Document Number FGDC-STD-013-2006, 290 p., 2 plates.
EPA Metadata Editor (EME), version 3.1.2, 2012; https://edg.epa.gov/EME/Home.htm

24. Thank You!
Questions?