Map Work and GIS
Why map work?
Maps are scaled drawings of the earth's surface. Kenya uses Survey of Kenya topographic maps (for example 1:50,000 sheets) for planning roads, farms and settlements.
Map scale
Expressed three ways:
- Ratio/representative fraction: 1:50,000
- Statement: 1 cm represents 0.5 km
- Linear: a ruler line divided into km
Worked example: A road measures 6.2 cm on a 1:50,000 map. Actual distance = 6.2 x 0.5 = 3.1 km.
Direction and bearing
Direction uses the compass points. A bearing is measured clockwise from north (0 to 360 degrees). A town due east has a bearing of 090 degrees.
Grid references
The map is covered by a square grid. Four-figure references name a grid square; six-figure references locate a point to 100 m. Always read eastings first, then northings.
Representing relief
- Contours: close lines mean steep slope; wide apart mean gentle slope.
- Spot heights and trigonometrical stations.
- Form lines (dashed) and hill shading.
- Features: ridge, valley, spur, escarpment, plateau.
Cross-sections and gradient: gradient = vertical interval / horizontal distance. Vertical exaggeration = vertical scale / horizontal scale.
Area calculation
- Regular shapes: use geometry.
- Irregular shapes: count full squares plus half of the partial ones; each square on a 1:50,000 map is 1 km2.
Map interpretation
Describe relief, drainage (rivers, lakes), vegetation, settlement patterns (nucleated, linear, dispersed), transport networks, and economic activities (farming, trading). For example, a map of Kisumu shows a lake port, a railway terminus and a dense settlement on flat land.
Photographs and fieldwork
Aerial photographs and satellite images supplement maps. Fieldwork steps: statement of the problem, hypotheses, data collection (questionnaire, observation, sketching), analysis, report.
Geographic Information Systems
GIS stores spatial data in layers and links it to attribute data. Components: hardware, software (QGIS, ArcGIS), data, people, methods.
Data types: vector (points, lines, polygons) and raster (pixel grids).
Uses in Kenya:
- Mapping land use and parcels (Ardhi Sasa).
- Tracking drought and food security using satellite data.
- Planning roads and water supply.
- Monitoring wildlife in Maasai Mara and Tsavo.
- Disaster management for floods in Budalangi.
GPS gives location using satellites, and remote sensing collects data from a distance.
Try it
- Use a 1:50,000 sheet to give a six-figure reference of your school.
- Calculate the gradient between two points 800 m apart and 40 m in height difference.
- List three layers you would include in a GIS map of a flood-prone area.