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Geographic
Data

Master the tools geographers use to collect, analyze, and represent spatial information about the world around us.

AP Human Geography

What Is Geographic Data?

Geographic data is information about locations, places, and spatial relationships on Earth's surface. It connects what exists or happens to where it exists or happens: every data point is tied to a specific position in space.

Two Core Types of Geographic Data

Qualitative (Categorical)
Describes characteristics of a place: language spoken, religion, land use type, political boundaries. Answers "what kind?"
Quantitative (Numerical)
Measures amounts or values at locations: population density, rainfall in mm, elevation in meters. Answers "how much?"

Spatial Data Models

Vector Model Points Lines Polygons Raster Model Grid of cells (pixels) Each cell stores one value

The Power of GIS

A Geographic Information System (GIS) is software that captures, stores, analyzes, and displays geographic data in layers. Each layer represents a different type of information about the same area.

Locations Roads Water Land Use GIS Layer Stack

GPS and Remote Sensing

GPS
Global Positioning System: a network of satellites that provide precise latitude, longitude, and elevation coordinates for any point on Earth.
Remote Sensing
Collecting data about Earth's surface from a distance: satellites and aerial platforms capture images using visible light, infrared, or radar.

Scales of Analysis

Local Neighborhood or city level National Country-wide patterns Global Worldwide comparisons Increasing scale of analysis →

Absolute vs. Relative Location

Absolute Location Relative Location
Definition Exact position on Earth's surface Position relative to other places
System Latitude/Longitude, street address Directional, distance-based
Example 40.7° N, 74.0° W "Near the harbor"
Changes? Never changes Changes with context
Data Type Quantitative Qualitative

Essential Map Types

Reference
Shows locations of features: political boundaries, roads, cities. Think road maps and atlas pages.
Thematic
Shows spatial patterns of a specific topic: choropleth, dot density, isoline, and cartogram maps.
Cadastral
Shows property boundaries and land ownership. Used in legal and tax contexts for parcel-level detail.

Thematic Map Subtypes

Choropleth
Shaded regions show magnitude. Example: states colored by population density.
Dot Density
Each dot represents a set number. Example: one dot = 10,000 people.
Isoline
Lines connect equal values. Example: contour lines for elevation or isobars for pressure.
Cartogram
Area size is distorted to represent a variable. Example: countries sized by GDP.

How to Analyze Geographic Data

1
Identify the data type. Is it qualitative (categories) or quantitative (numbers)?
2
Determine the scale. Are you looking at local, regional, national, or global patterns?
3
Read the legend and source. What do colors, symbols, or sizes represent? Who collected this data?
4
Look for spatial patterns. Clusters, gradients, outliers: where are values highest or lowest?
5
Explain the pattern. Connect the spatial distribution to geographic processes (migration, urbanization, climate).

Example: Reading a Choropleth Map

Region A
\( 12/\text{km}^2 \)
 Region B
\( 85/\text{km}^2 \)
 Region C
\( 240/\text{km}^2 \)
 Region D
\( 510/\text{km}^2 \)
\( \text{Population Density (people/km}^2\text{)} \)
 Low High

Example: Census vs. Survey Data

Census Sample Survey
Coverage Entire population counted Representative subset
Frequency Every 10 years (U.S.) Annual or ongoing
Cost Very high Lower
Detail Basic demographics Deep topical questions
Accuracy Complete but may undercount Margin of error exists

Example: Calculating Population Density

Population density measures how many people live per unit of area. The formula is straightforward:

Practice problem: Country X has a population of 50,000,000 people and a land area of \( 200{,}000 \text{ km}^2 \).

Common Mistakes

✕ Confusing Map Types
Calling a dot density map a "choropleth" because both show quantity. Choropleth uses shading; dot density uses individual dots.
✕ Ignoring Scale
Drawing conclusions about local patterns from national-scale data. Aggregated data hides local variation (ecological fallacy).
✕ Mixing Up Density Types
Using arithmetic density when physiological density is more appropriate for comparing food production capacity.

Summary: Geographic Data at a Glance

Concept Key Idea Example
Qualitative Data Categories, descriptions Land use type
Quantitative Data Numeric measurements Population count
GIS Layered spatial analysis Overlay tool
GPS Precise coordinates Lat/Long fix
Remote Sensing Data from a distance Satellite imagery
Choropleth Map Shaded regions by value Income by state
Scale of Analysis Local → Global scope City vs. country

Question 1 of 5

Which type of thematic map uses shaded areas to represent the magnitude of a variable across regions?

Question 2 of 5

A geographer uses satellite imagery to monitor deforestation rates in the Amazon. This is an example of:

Question 3 of 5

Country Y has a population of 30 million and a total land area of \( 120{,}000 \text{ km}^2 \), of which \( 40{,}000 \text{ km}^2 \) is arable. What is its physiological density?

Question 4 of 5

A GIS analyst overlays a flood zone layer with a residential housing layer. The primary purpose of this overlay analysis is to:

Question 5 of 5

The coordinates 34.0522° N, 118.2437° W describe the location of Los Angeles. This is an example of: