Cartographic and statistical techniques: maps, graphs, photographs and data analysis
Domain 8 tests technique: whether you can read a map, a graph and a photograph quickly and convert units without error.
Maps
- Scales: 1:25 000 (MTN25), 1:50 000 (MTN50), 1:200 000, 1:1 000 000. A larger denominator means a smaller scale and less detail.
- Conversion: 1 cm on a 1:50 000 map equals 50 000 cm, that is 500 m or 0.5 km.
- Contours: note the interval and the index contours; slope = Δh / horizontal distance × 100 for a percentage.
- Projection: Spanish official mapping uses UTM on ETRS89; latitude and longitude are given in degrees; distortion grows away from the central meridian.
Graphs and statistics
- Choropleth (values per administrative unit), isopleth (isohyets, isotherms and other continuous fields), dot maps, flow maps and cartograms.
- Gaussen climatic diagram: precipitation and temperature plotted at a 1:2 ratio, arid when P < 2T.
- Population pyramid, Lorenz curve and Gini coefficient for concentration, triangular graph for three-part composition.
- Rates: birth rate = births / total population × 1 000; density = population / km²; index number = value / base value × 100.
Photographs
Read in layers - foreground, middle ground, background - then identify relief, vegetation, water, land use and settlement pattern, and finally infer climate and human pressure. Vertical aerial photographs and satellite images (Sentinel-2, Landsat) support this, with NDVI as a proxy for vegetation vigour.
Worked example
On a 1:25 000 map, two points are 6.4 cm apart and lie on the 1 150 m and 1 050 m contours. Real distance = 6.4 × 25 000 = 160 000 cm = 1.6 km. Slope = 100 / 1 600 = 0.0625, i.e. 6.25 %, about 3.6°. Interpretation: a gentle slope consistent with a cuesta or a campiña, not a mountain front.
Traps
- Dividing by 100 instead of 1 000, or forgetting to convert centimetres to metres.
- Confusing choropleth with isopleth.
- Using arithmetic density when physiological density is requested.
- Giving a slope without units, or in percentages when degrees are asked for.
- Describing a photograph without stating what it implies.