4.1(a), 4.1(c)–(e); 4.2(a)–(b) - Geographical evidence, maps and GIS

What makes evidence geographical

Information becomes geographical when its location and relationships to other locations help answer a question. A beach-pebble diameter is a measurement; a diameter recorded at a stated position along a sediment cell can help investigate sorting during transport. Location alone is not an explanation: a geographer asks why a pattern occurs, at what scale, and whether different processes could produce it.

Two different distinctions describe evidence. Quantitative information records amounts, counts or numerical measurements, such as a settlement's population or channel width. Qualitative information records meanings, experiences or qualities, such as a resident's account of belonging. A coded interview can produce counts, but those counts do not preserve every meaning in the original account. Neither numerical appearance nor a detailed quotation guarantees accuracy.

Primary and secondary describe a relationship to the investigation. Researchers commonly call information they collect themselves primary and evidence produced for another purpose secondary. OCR's investigation definition also recognises unmanipulated raw datasets as primary data. Therefore explain the evidence's actual provenance rather than assuming that everything downloaded is secondary. An edited published interpretation and its underlying untouched observations are different information products.

Evidence may be numerical without being spatial, or both: a table of noise readings becomes spatial when readings have coordinates. Digital photographs contain visual evidence; maps show selected spatial relationships; diagrams simplify processes; graphs emphasise distributions and change. Factual reports and creative sources such as poems can both reveal place, but they support different claims. A poem may illuminate an experience of exclusion without estimating how many residents share it.

Reading maps at different scales

A map selects and generalises features of the Earth, so its scale, symbols and date determine what questions it can answer. A large-scale map shows a smaller area in greater detail.

Worked map distances

On an original $1:25\,000$ map, a 4-centimetre straight line represents:

On a separate $1:50\,000$ map, a 3.6-centimetre route segment represents:

Follow a curved route in short measured segments rather than using its endpoint distance. Screen zoom changes displayed size, so use the current scale bar rather than a remembered paper measurement.

Read coordinates in the stated coordinate system. On a British National Grid map, eastings are read before northings; six-figure grid references refine a location within a kilometre square. Latitude and longitude instead express angular position. Do not overlay two datasets merely because both have two columns of coordinates: their reference systems and units must be compatible.

Contours join equal elevations. Closely spaced contours normally indicate a steep slope, but compare the contour interval and map scale first. A sequence of contour values is needed to distinguish rising ground from a depression. These observations help explain drainage routes and the exposure of settlements, rather than proving a hazard occurred.

Worked population densities

Illustrative areas: A contains 200 residents in $1\,\mathrm{km^2}$; B contains 300 in $3\,\mathrm{km^2}$. Divide population by area before comparing:

B has more people but lower density. In a second comparison, C has 850 residents in half a square kilometre and D has 2400 in two square kilometres:

The larger total again does not identify the denser area. A choropleth shades whole areas and usually needs a rate, proportion or density when areas differ in size. A shaded ward does not show every household's circumstances. ONS's choropleth guidance explains this choice; its Census maps guidance, updated May 2023, warns that displayed statistics describe an area rather than the building beneath a label.