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

INTRODUCTION

COMMON TASKS

• Converting raster maps to vectors

• Scanned paper maps

• Digital raster images

• Cleaning up vector messes

• Symbolizing

• Attributing

• Metadata

• Publishing Raster Source

Vector Lines

Polygons

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

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

MAP EXAMPLE

MAP EXAMPLE

MAP EXAMPLE

Unit overruns

fault contact

Gaps

Overshoot

Overshoot Map features

extend beyond

boundary

Gaps

UNCLOSED POLYLINES

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.

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…

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??

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

STEP 2: ORGANIZE YOUR DATA

• Develop an organized file structure

• Use a descriptive and progressive file naming convention

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

• Save often!!!!

Points

Separates

Geologic Lines

Geologic Polygons

• ArcGIS + ET GEOWIZARDS

STEP 4.1: LINES TO POLYGONS

Build Polygon

Tool

Shapefile

Lines v1

ET

Geowizards Polygon v1

• ArcINFO

STEP 4.2: LINES TO POLYGONS

Feature to

Polygon

Shapefile

Lines v1 ArcToolbox Polygon v1

Construct

Polygons Topology Rules

Geodatabase

Lines v1 Editor

Toolbar

GDB

Polygon v1

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)

STEP 5.2: THE EDITING PROCESS

Polygon v1

Topology Edits

Editor Toolbar Polygon v2

Feature to Point • Preserve Attributes

• Choose Inside

Option

ArcToolbox

Points v1

Line v2

Line to Feature • Import attributes

from Points v1

ArcToolbox

Polygon v2

Edits

Lines v1

Option 1

Option 2

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

STEP 7: METADATA

• Take time to write thorough metadata

• Know what format your users are using

• Use a metadata editor

• ArcCatalog

• EPA Metadata Editor

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

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

Thank You!

Questions?