Fieldwork and skills, Year 8: more practice

A higher value

提示The key links each shade to a range of values.

为什么Choropleth maps use a graded colour scheme, usually light for low values and dark for high ones, so the pattern is visible at a glance.

Population density (people per square kilometre)

提示Totals depend on how big the region is.

为什么Density divides the number of people by the area, so large and small regions can be compared fairly. Choropleth maps work best with rates, ratios or densities.

Variation within the region

提示Each area gets a single colour.

为什么A region shaded dark may contain both very high and very low places. The map shows the average, not the differences inside.

25

提示Share the full range equally between the classes.

为什么100 ÷ 4 = 25, so the classes are 0 to 25, 25 to 50, 50 to 75 and 75 to 100.

The order of the shades makes higher and lower values easy to read

提示Think about reading the map without checking the key every time.

为什么A single-colour range has a natural order. Mixed colours have no obvious order, so the reader must keep looking back at the key.

How many people live in areas at risk of flooding

提示Think about what two sets of information show together.

为什么Overlaying means viewing layers on top of each other. Patterns that are hidden in one layer on its own appear where layers meet.

Geographic Information System

提示The last word is about how the data are organised.

为什么A GIS stores, layers and analyses location data on a computer, such as roads, rivers, schools and flood zones.

A layer can be updated without redrawing the whole map

提示Think about how a paper map gets out of date.

为什么The roads layer can be replaced with a newer version while the rivers layer stays the same, and layers can be switched on or off.

Vector

提示A raster layer is a grid of pixels.

为什么Points, lines and polygons are all vector data. A lake drawn as a polygon is vector; a satellite photo is raster.

B: many homes far from any library

提示Combine the two layers rather than reading each alone.

为什么Overlaying the layers shows crowded areas that are far from any library. This is how a 'where should it go?' question is answered.