Key Points

Introduction to Foundations

  • Python (in Jupyter notebooks on Google Colab) is for repeatable data work; QGIS is for looking at data and making maps
  • Save your own copy of each notebook, and run cells in order with Shift + Enter
  • Colab sessions and files are temporary; data is always read from the web
  • This module prepares you for every other module in the curriculum

Python Basics

  • Run cells with Shift + Enter, in order, and read the last line of any error first
  • Values have types (int, float, str, bool); convert numbers stored as text before doing math
  • Lists keep values in order (from position 0); dictionaries look values up by key
  • if / elif / else make decisions; for loops repeat work; functions package work for reuse

Working with Data

  • pandas reads tables from the web into DataFrames with pd.read_csv(url)
  • Check data types first; keep identifiers such as FIPS codes as text
  • Select, filter, sort, calculate and group with a few lines of code, no loops needed
  • Pick the chart that answers the question, and always label it

Geospatial Python Basics

  • A GeoDataFrame is a pandas DataFrame plus a geometry column; gpd.read_file() reads it from the web
  • Check .crs first; use to_crs() to a projected CRS in meters before measuring, and set_crs() only to label missing CRS information
  • Attribute joins match IDs (make them the same type first); spatial joins match locations (same CRS first)

Getting Started with QGIS: Your First Map

  • Add Vector Layer with the HTTP(S) protocol loads data straight from a web address.
  • The attribute table holds the data behind every styling choice.
  • Use Categorized for categories and Graduated for numbers, and compare classification modes.
  • A Print Layout combines the map with its title, legend, scale bar, north arrow and source.
  • Save the project often; export layouts as PNG or PDF.
  • Check layer and project coordinate systems before measuring anything.