Page 84 - Nutrient Management Planning Guide

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Chapter 3.2

Table 3.2.2 Map Scales and Conversions

Map Scale

Map cm Ø Actual m

Actual km Ø Map cm

Map inches Ø Actual feet/miles

Actual miles Ø Map inches

1:10,000 × 100 × 10 × 833.33 (ft) × 6.34 1:12,000 × 120 × 8.33 × 1,000 (ft) × 5.28 1:15,000 × 150 × 6.67 × 1,250 (ft) × 4.22 1:50,000 × 500 × 2 × 0.789 (mi) × 1.27 1:100,000 × 1,000 × 1 × 1.58 (mi) × 0.63

Adapted from McNeil et al., 1998b

tip

Remember that

distances and dimensions distort as you move from the centre of the image to the edge of the photo.

Estimating Areas and Distances Using an Aerial Photo

Aerial photos can be used to estimate distances and areas with simple equipment and calculations. To aid in the calculation of distances and areas, nine of the commonly used or available air photo scales are listed in Table 3.2.4 and Table 3.2.5. For each of the common scales, table 3.2.4 reports the distance on the ground for each one cm measurement on the photo, the cm measurement for each km, the number of hectares per square cm and the number of hectares represented by each dot on an acreage grid map (64 dots per square inch). For each scale table 3.2.5 reports the distance on the ground for each one inch measurement on the photo, the measurement for each mile, the number of acres per square inch and the number of acres represented by each dot on an acreage grid map (64 dots per square inch).

An example of a partial acreage grid map is illustrated in Figure 3.2.1. A grid map will be made up of multiple rows and columns segmented into one inch by one inch squares. Each square contains 64 evenly spaced dots. The size of the grid map can vary depending on its application. The larger the photo, the larger the grid map may be. Appendix 3 contains a grid map that is seven columns wide by seven rows deep. This may be photocopied onto a transparency and used to determine areas on a photograph.