Appendix 1 1(b), 2(c) - Images and spatial representations

Viewpoint and selection

An image records a view of a place from a particular position and time. Its evidence depends on what lies inside the frame, what is hidden and how the image has been selected or processed.

Perspective makes near objects appear larger. Counting visible buildings in a ground photograph is not a population-density measurement. A vertical view usually supports mapping more directly, but relief and camera geometry still produce displacement unless corrected. An oblique view may show a cliff and its hinterland together while hiding land behind the cliff.

Before interpretation record source, acquisition date, location, direction, scale or spatial resolution and processing. Publication date is not necessarily acquisition date. Compare a morning weekday street photograph with a weekend evening image cautiously: apparent activity differences may reflect timing rather than long-term change. A promotional photograph and a resident's photograph can show different valid aspects of the same place because their purposes and framing differ.

Observation, inference and field sketches

Systematic interpretation begins with what is visible and then tests possible explanations. In an original illustrative photo description, a river bends beside a town, paved streets reach its banks, and a strip of trees separates some buildings from the channel. These are observations. “The trees prevent flooding” is an inference: the image alone does not establish their effect, flood height or drainage capacity.

Use shape, size, colour or tone, texture, pattern, shadows and association together. A regular grid of roofs suggests a planned layout; it does not establish income or tenure. Shadows help identify relief and object height but can obscure land cover. Pale bare ground may be dry sediment, salt, sand or a construction surface. Check the scale, neighbouring features and other sources before assigning a class.

A field sketch selects important features from a view to communicate relationships. Establish viewpoint, orientation and date; draw the main outlines and foreground/middle/background or land-use zones; use clear leader lines for labelled features; annotate processes cautiously. Keep a visible building outline separate from an inferred use. For the river example, label “trees beside channel” as observed, then separately note “possible roughness/barrier effect; requires evidence”. The sketch is a purposeful simplification, not a photograph substitute for measuring every feature.

Two observers can classify the same image differently. State categories in advance, record ambiguous features, and compare interpretations. A repeated fixed viewpoint helps monitor change, but leaf cover, lighting and weather may still change what appears visible.

Satellite resolution and classification

A satellite sensor measures radiation rather than directly recording categories such as forest or settlement. Analysts select bands, process values and interpret them with reference data.

Spatial resolution describes the ground detail represented by a pixel. A 30 m pixel covers 900 m²; a narrow road may contribute only part of its signal. Spectral resolution concerns the wavelength bands recorded; a false-colour display assigns selected bands to screen colours. Red in a false-colour vegetation image is not proof of fire: the band combination and legend determine its meaning. Temporal resolution concerns repeat observation opportunities, while cloud may reduce usable optical observations. Greater spatial detail does not automatically give more frequent or more accurate observations.