Maps, spatial data and fieldwork
Shared geographical foundations
This chapter reviews shared geographical concepts and interpretation of supplied evidence. It does not establish the syllabus, administrative rules, current policy, language or difficulty of a particular examination.
Core rules and concepts
- Map basics: scale = map distance / real distance. 1:25,000 means 1 cm = 250 m; a measured 4 cm on the map equals 1 km in reality. Contour lines: read the stated contour interval and any supplementary contours, so closer lines mean steeper slopes; slope percent = vertical difference / horizontal distance × 100. A cross-section follows the specified transect, which need not be the steepest-ascent line.
- Thematic maps: distinguish choropleth maps (area-level attributes, commonly normalized rates or densities per administrative unit; sensitive to unit size and to the ecological fallacy), isopleth maps (interpolated continuous values), dot maps (absolute distributions, but dot value choice distorts), and propotional symbols. Always state map date, source and classification method; class breaks change the apparent pattern.
- Statistics: mean, median, standard deviation; correlation versus causation; absolute versus relative rates. Standardise when comparing populations of different sizes. Read time series for trend, cycle and outliers.
- Remote sensing: interpret colour composites (healthy vegetation often has high near-infrared reflectance, with display appearance depending on the chosen bands and color assignment), spatial and temporal resolution trade-offs, and change detection by differencing images. Aerial photographs support land-use mapping; satellite data support large-area monitoring.
- Fieldwork design: define question, sampling strategy (random, systematic, stratified), measurement instruments and error sources, a control, and documentation for reproducibility. Questionnaires need pre-tested wording and awareness of response bias. GIS layers (points, lines, polygons) allow overlay and buffer analysis.
Worked example with reasoning
Task: a choropleth map shows high nitrate values in a rural district. Explain whether that proves high nitrate in every field. Reasoning: choropleth maps aggregate to administrative units, so internal variation is invisible; the value may be driven by a few intensive farms or by a single monitoring station. The correct chain is: understand the indicator (what exactly is measured, where), check unit size and classification, check the date and source, then look for within-unit data. Only then can you claim a pattern. This converts a visual impression into a methodologically defensible statement.
Traps that cost marks
- Reading a scale as a fixed ratio of map centimetres to kilometres without converting consistently.
- Interpreting contour spacing backwards (closer = steeper, not flatter).
- Taking choropleth patterns as evidence about individuals (ecological fallacy).
- Comparing absolute counts across units of different size.
- Describing a remote-sensing image without stating resolution, date or band combination.
- Designing fieldwork with no sampling strategy or error discussion.