Things You Need to Know About GIS Data on Your Computer

Introduction

Understanding how to work with spatial data formats and naming conventions is crucial for successful GIS work. This lab will teach you about different data formats, proper naming strategies, and how to recognize spatial data in unexpected places.

Learning Objectives

By the end of this lab, you will be able to:

  • Apply GIS-compatible file naming conventions
  • Understand different spatial data formats and their trade-offs
  • Recognize spatial data in non-spatial formats
  • Choose appropriate formats for different GIS tasks

File Naming Conventions

Use Esri Raster naming rules as your universal standard - they represent the most restrictive (and finicky) naming requirements in GIS, so following them ensures compatibility across all software.

The Esri Standard (Least Common Denominator)

Esri has the strictest naming requirements in GIS. Following their official rules (Esri Community: How to Name Things in ArcGIS) ensures universal compatibility:

The Official Esri Rules:

  1. Avoid spaces and most special characters in pathnames and filenames

    • No spaces, &, -, or other special characters
    • Underscores (_) are allowed and encouraged as space replacements
    • These restrictions prevent cryptic failures in processing

  2. Keep pathnames under 128 characters total

    • Windows absolute pathname limit is 260 characters
    • Shorter paths prevent mysterious errors

  3. Start with a letter always

    • Never begin with numbers or non-alphabetic characters
    • Applies to files, folders, fields, and all GIS objects

  4. Avoid SQL reserved words

    • Skip: OBJECTID, VALUE, COUNT, NOT, OR, ON, IN, OVER, SELECT
    • Prevents confusion in database operations

  5. Keep field names ≤ 10 characters

    • This is a dBase (.dbf) limit affecting shapefiles
    • Use aliases for longer descriptive names

  6. Raster names ≤ 14 characters

    • Must start with letter (critical for raster datasets)
    • Special characters in paths cause export failures
    • Grid format compatibility requires this limit

  7. Path length matters

    • Full file paths should stay well under 256 characters
    • "Flatten" deep folder structures to avoid issues

Good Esri-compatible names:

  • Pop_Dens2020.tif (uses underscore to replace space)
  • Elev_12m.tif (underscore separates words)
  • Land_Cover.shp (underscores allowed and encouraged)
  • Roads_2024.gpkg (follows all rules with underscores)

Names that break Esri compatibility:

  • elevation-12m.tif (hyphen causes raster export failures)
  • 2020_population.tif (starts with number - will fail)
  • land cover data.shp (spaces cause cryptic errors)
  • COUNT.shp (SQL reserved word causes confusion)
  • VeryLongRasterDatasetName.tif (over 14 characters)
  • pop&density.tif (ampersand causes failures)

Practical Implementation

When naming is out of your control:

  • Downloaded datasets often have non-compliant names
  • Rename immediately upon extraction
  • Document original names if needed for reference

Recommended naming strategy:

  1. Replace spaces with underscores: Land Cover → Land_Cover
  2. Abbreviate intelligently: Temperature → Temp, Precipitation → Precip
  3. Use underscores for readability: Pop_Dens_2024 instead of PopDens2024
  4. Embed key info with separators: Roads_2024, Elev_30m
  5. Version with underscores: Model_v1, Test_2024

Why this matters (from Esri's official warning):

  • Prevents cryptic error messages: Raster tools fail with "999999" errors
  • Avoids export failures: Special characters break raster processing
  • Enables reliable scripting: ArcPy validates names automatically
  • Prevents "tempting fate": As Esri warns - violations "may work" but cause unpredictable failures
  • Universal compatibility: These rules work across all GIS software

Special considerations:

  • Database fields: Same rules apply to column names in attribute tables
  • Project files: Apply to .qgz, .aprx, and other project file names
  • Folder names: While less critical, consistency helps with scripting

Basic File Organization for GIS

Understanding how to organize and recognize spatial data files is fundamental for efficient GIS work. While detailed format specifications are covered in Week 01, here are the basics you need to know for file management.

Recognizing Spatial Data Files

Multi-file formats (keep together):

  • Shapefiles: Look for .shp, .shx, .dbf files with the same name

  • For Example:

    roads.shp, roads.shx, roads.dbf

    all belong together

Single-file formats:

  • GeoJSON: .geojson files
  • GeoTIFF: .tif or .tiff files with spatial information
  • GeoPackage: .gpkg files

Folders that are actually datasets:

  • File Geodatabase: .gdb folders (treat as single units)

File Organization Best Practices

Create a logical folder structure:**

Project_Name/
├── data/
│   ├── raw/          (original downloads)
│   ├── processed/    (cleaned/modified data)
│   └── outputs/      (analysis results)
├── maps/
├── scripts/
└── documentation/

Keep related files together:

  • All shapefile components in the same folder
  • Metadata files with their datasets
  • Projection files (.prj) with their data

Document your data sources:

  • Keep a simple text file listing where data came from, or get REALLY motivated and use Zotero!
  • Note download dates and any modifications made

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