What a topographic map shows
Topographic versus other maps
| MAP TYPE | SHOWS |
|---|---|
| Topographic | The shape of the land, plus natural and built features |
| Political | Borders and administrative areas |
| Thematic | One subject — rainfall, population, soil type |
| Road atlas | Routes for driving, with terrain simplified away |
The defining feature of a topographic map is that it shows relief — the third dimension, height, represented on a two-dimensional sheet.
How relief is shown
| METHOD | HOW IT WORKS |
|---|---|
| Contour lines | Lines joining points of equal height — the primary method |
| Spot heights | A dot with a number giving exact elevation |
| Trigonometrical stations | Surveyed points, often on summits |
| Hill shading | Simulated shadow suggesting three dimensions |
| Layer tinting | Colour bands for height ranges — green low, brown high |
| Hachures | Short lines down slopes; used on older maps |
Contours carry the actual information; the rest are visual aids.
The marginal information
The margins are not decoration — they are the instructions, and exam questions frequently depend on them.
| ELEMENT | WHY IT MATTERS |
|---|---|
| Title | What area is covered |
| Scale | Both as a ratio and as a scale bar |
| Contour interval | The height difference between adjacent contours |
| Legend or key | What each symbol and colour means |
| North arrows | True, grid, and magnetic north |
| Grid reference system | Which grid is used, and how to quote it |
| Date of survey and revision | How current the map is |
| Sheet number and adjoining sheets | Which map continues at each edge |
Always check the date. Roads, buildings, forestry, and watercourses change. A map surveyed decades ago is still accurate for landform and useless for finding a new bypass.
Always check the contour interval before interpreting slope. The same-looking pattern means something very different at 5 m intervals than at 50 m.