# TOPOGRAPHIC SURVEYING AND MAPPING

#### Topographic Survey:

- Determine position of natural and man made features

- Features drawn to scale on plan or map

- Determine ground elevations (contours, cross-sections and profiles)

- Vast majority done by aerial survey

- EDM and total station (x-y zontal location) and vertical location (elevation) by one sighting

- Rectangular and polar surveying techniques

- Rectangular technique: - Right angle off sets for location detail

- Cross section for elevation and profiles

- Polar technique use stadia or electronic techniques

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#### Scales and Precision:

Scale: Ratio between plan distance and ground distance

Consistent through the plan

Equivalences e.g. 1โ = 50โ

Fractions e.g. 1 : 500

Table 8.1

Small scale and intermediate scale done by aerial survey

- Reason for survey determine appropriate precise technique

- If points to be plotted on at scale 1:500 --> precision 0.25 m

- If points to be plotted on at scale 1:20,000 --> precision 10 m

- Some details can be precisely determined -->e.g. bldg corner

- Some details cannot precisely determined -->e.g. stream banks

- Some details can be determined with moderate precision ยฎ e.g. single large tree

Details that can be well defined is located with more precision then is required just for plotting because:

- It take little effort

- Uniform practice

- Some details are shown as layout dimensions

- If area contain only natural feature, stadia is used

- All topographic surveys are tied into both horizontal and vertical control (Benchmark)

- Horizontal control could be:

ยท - Closed transverse

- Transverse from coordinate grid monuments

- Close to another coordinate grid monuments

- Route centerline

- Assumed baseline

- Measurement taken to establish control are more precise than other measurements

- Control should be accurate and well references

- Control should be used for additional work (e.g. layout)

#### Location by Right Angle Offset

- Used in all topographic survey except mapping

- Provide location of details and area elevation taken by X-section

- Measure distance to base line and station on baseline

- Baseline laid by stakes (nails) each 100โ or 20/30 in,

- Sketch in note book

- Tape can be laid on baseline if terrain is smooth

- Details on both sides of baseline or make split baselines

- Penta prism or (swing-arm technique (Appx.)

- SAT good result for short of test 15 m otherwise use penta prism or transit

#### Cross Section and Profile

- Cross section to he baseline

- Profile along the baseline

- Elevation plotted as spot elevation, contours or end area for construction quantity estimation

- Intervals 20/30 in. โ in changing terrain 10-15 m + any sudden change in terrain (top, bottom of slops)