Introduction
Surveying is a key process in fields like civil engineering, construction, and geography, involving the precise measurement of distances, angles, and positions on or near the Earth’s surface. This data is used to create maps, determine boundaries, and plan construction layouts. Let’s delve into the basics of survey, including its definition, types, units of measurement, scale types, and commonly used symbols.
Table of Contents
Definition
It is the practice of determining the relative positions of points on, above, or below the Earth’s surface. This is achieved through careful measurement and data collection, which are then represented in maps, plans, or digital models. Survey is crucial for creating accurate maps, defining property boundaries, planning roads, and other urban and rural development projects.
Types
It can be categorized by its purpose, the area being surveyed, and the techniques used. Below are some common types of survey:
By Purpose
Geodetic Survey: Conducted over large areas, taking the Earth’s curvature into account. It’s used for projects like national borders and large infrastructure with highly accurate mapping, based on a network of control points.
Plane Survey: Assumes the Earth’s surface is flat over small areas. Used for smaller projects like land subdivision, roadwork, and building layouts.
By Method
Chain Surveying: Simple tools like chains or tapes are used to measure distances, suitable for smaller, open areas.
Compass Surveying: Uses a compass to determine directions between points. This method is useful for rough surveys over areas with obstructions.
Theodolite Surveying: Uses a theodolite to measure both horizontal and vertical angles, providing more precise measurements than compass survey. Commonly used in construction.
Photogrammetric Surveying: Uses aerial photographs to survey large areas from above, like cities or forests.
GPS Surveying: Utilizes satellite technology to get exact locations on the Earth’s surface. It’s widely used today for its convenience and accuracy.
By Object of Surveying
Topographic Survey: Focuses on mapping land features like hills, rivers, and vegetation.
Hydrographic Survey: Surveys bodies of water, measuring depths and charting underwater features.
Cadastral Survey: Defines and records property boundaries for legal documentation.
Engineering Survey: Provides accurate measurements and maps for construction sites, including roads, bridges, and buildings.
Units of Measurement
Survey requires consistent units to accurately measure distances, angles, and elevations. Commonly used units include:
Linear Measurements
Metric: Meters (m), centimeters (cm), and millimeters (mm).
Imperial: Feet (ft) and inches (in), commonly used in the United States.
Angular Measurements
Degrees (°), minutes (‘), and seconds (“) are used for measuring angles.
Radians, though less common in basic surveying, are sometimes used in advanced applications.
Elevation or Altitude
Measured in meters or feet above mean sea level (MSL).
Accurate measurements are vital in surveying, as errors can lead to significant inaccuracies in projects. Hence, precision is always prioritized.
Scale in Surveying
The scale shows the relationship between a map’s measurements and the actual distances on the ground, making large areas manageable to represent on paper. Different scale types in surveying include:
Graphical Scale: Shown as a bar on the map, divided into equal sections marked with units of measurement. It allows for easy measurement without calculations, as the scale adjusts to the map’s size.
Shrunk Scale: Used when a map’s original size has changed due to paper shrinkage or stretching, affecting the measured distances. To ensure accuracy, the shrunk scale adjusts based on the map’s current measurements.
Representative Fraction (RF): A ratio that represents the map’s scale. For example, an RF of 1:10,000 means 1 unit on the map equals 10,000 units on the ground.
Conventional Signs
Conventional signs are standardized symbols that represent different features on maps, making them easy to read and interpret. Common symbols include:
Buildings: Often represented by rectangles or simple shapes.
Roads: Shown as solid or dashed lines, with variations in thickness for different types (e.g., highways, streets).
Rivers and Lakes: Represented by blue lines or shaded blue areas.
Trees and Forests: Displayed as small circles or clusters to indicate wooded areas.
Railways: Shown as parallel lines with cross marks.
Contour Lines: Represent elevation or depth, with close lines indicating steep slopes and widely spaced lines indicating gentle slopes.
These symbols help map readers quickly understand features without needing detailed explanations and are standard in map reading.
Conclusion
Surveying is a vital process that supports the planning, building, and management of various projects. By understanding the different types of surveying, scales, and symbols, surveyors can create accurate maps and layouts. This ensures successful project planning, minimal errors, and effective land and resource management.
Frequently Asked Questions (FAQ)
What is the difference between a graphical scale and a shrunk scale?
A graphical scale appears as a bar on the map, allowing for easy measurement. A shrunk scale adjusts for maps that have changed size due to paper shrinkage, ensuring measurements remain accurate.
What units of measurement are used in surveying?
Distance is typically measured in meters (metric) or feet (imperial). Angles are measured in degrees, minutes, and seconds, while elevation is often noted in meters or feet above mean sea level.
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