Introduction to Cartography GEOG 2016 E

1. Introduction to CartographyGEOG 2016 E Lecture-4 Sources of Data

2. Cartographic Data and Surveying • To make a map we need data. • The cartographic data is generally obtained by surveying. • There are other methods too, such as • Remote Sensing, Census and Sampling • However, surveying is the most commonly used method of gathering data for generating maps. • Surveying is the method of determining the relative positions of points on, above or beneath the earth’s surface.

3. Categories of Surveying • Plane Surveying • Surveying with the reference base for fieldwork • Surface is assumed to be flat horizontal • Generally within a radius of about 20 km, the pull of gravity is nearly parallel – hence horizontal lines can be considered straight • Geodetic Surveying • To determine relative positions of widely spaced points, lengths and directions • Takes earth’s curvature into account

4. Survey Types • Photogrammetry • By camera or other sensors in airplanes or satellites • Topographic Surveying • Collecting data specifically for making maps • Route Surveying • For civil engineering projects, such as highways, railroads, pipelines etc. • Hydrographic Surveying • To map shorelines and the bottom of water bodies

5. Measuring Distance • Linear measurement is the basis of all surveying • Methods of measuring horizontal distance • Rough Measurements: Pacing, Odometer, Tacheometer • Accurate Measurements: Taping, EDM, GPS • EDM and GPS are the most commonly used methods for surveying

6. Taping • Applying the known length of a graduated tape directly to a line a number of times • Steps • Lining in: shortest distance between two points is a straight line • Applying tension: rear point of tape is anchored and tension is applied to the head • Marking tape lengths: each application of the tape requires marking using chaining pins • Reading the tape: the graduated tape must be read correctly • Recording distance: total length must be recorded accurately

7. Types of Tapes and Chains • Gunter’s Chain • 66’ long with 100 links with each link being 7.92 inches long • Developed by Edmund Gunter in 1600’s in England • Engineer’s Chain • Same construction as Gunter’s chain but each link is 1.0’ long

8. Types of Tapes and Chains • Surveyor’s and Engineer’s Tapes • Made of ¼” to 3/8” wide stell tapes in 100’, 200’, 300’ lengths • Multiple types of marking and graduation • Available in feet and metric • Invar Tapes • Made of special nickel steel to reduce length variations due to temperature changes • Extremely brittle and expensive • Used mainly for standard comparison of tapes • Cloth, Fiberglass, PVC Tapes • Lower accuracy • Used for measurements of 0.1’ accuracy

9. Slope Measurements • Generally, measurements are made horizontally • Often the distance can be measured directly on the slope • However vertical or zenith angle must be obtained • Horizontal Dist. = sin(zenith angle) x slope distance • Horizontal Dist. = cos(vertical angle) x slope distance Zenith Angle Slope Distance Vertical Angle Horizontal Distance

10. Taping Error • Instrumentation Error • Tape may be defective • Natural Error • Tape length changes due to temperature, wind or weight of the tape • Personal Error • Carelessness in setting pinsor reading tape

11. Transit • Transit is the most widely used surveying instrument • Used for measuring horizontal and vertical angles • Can also measure vertical and horizontal distances • Components • Alidade: upper part • Horizontal limb: middle part • Levelling-head: Lower part

12. Total Station • Modern version of transit with an electronic distance meter (EDM) • Electronic/optical instrument • Can measure slope distances from the instrument to a particular point • Extensively used in modern surveying

13. Levelling • Levelling is the determination of the elevation of a point or difference between points referenced to some datum • Terminologies • Datum: Any level surface to which elevations are referenced • Mean Seal Level (MSL): The average height of the surface of the sea for all stages of the tide over a 19 year period at 26 tide stations along Pacific, Atlantic and Gulf • National Geodetic Vertical Datum: Nationwide reference surface for elevations throughout the US

14. Levelling • Mostly mean sea level is used • MSL varies along the coast • Pacific is almost 2’ higher than Atlantic and Gulf • The level surface parallels the curvature of the earth • Hence a level line is a curved line • Generally measured with the Automatic or Self-levelling level

15. Differential Levelling • Also called Spirit Levelling • Most common type of levelling • Determines the difference in elevation using a horizontal line of sight and readings on a graduated rod

16. Topographic Surveying • Process of: • determining the positions of the natural and artificial features on the earth’s surface • Determining the configuration of the terrain • Planimetry • Location of features • Topography • Configuration of the ground

17. Topographic Surveying • Scale and accuracy • Depend on the instrument used and method • Presentation method • Contour Lines: Imaginary line on surface of the earth passing through points that have equal elevation • Contour Intervals: Vertical distances between lines • Index Contour: Every 5th contour drawn heavier on maps • Slopes can be obtained from contours

18. Topographic Surveying • Interpolation • Can find elevation of any point • Or find a contour line with known elevation of a point • Contour Characteristics • Each contour must close within a map or outside its borders • Contours do not cross or meet except in caves, cliffs and vertical walls • Contour lines crossing streams form V’s pointing upstream • Contour lines crossing a ridge form U’s pointing down the ridge

19. Methods of Topographic Surveying • Factors that influence the choice of method • Scale of the map • Contour interval • Type of terrain • Available equipment • Accuracy required • Extent of area to be mapped

20. Methods of Topographic Surveying • Cross section • Railroad or highway • Equipment used: transit, tape and level • Trace contour • Drainage or impoundments • Involves finding elevations at different points using transit • Grid • Small areas • The smaller the grid, the better the accuracy • Controlling point • Large area, plane table • Positions and elevations of pre-selected control points • EDM • Radial • Equipment: total station

21. Errors in Topographic Surveys • Improper selection of contour interval • Improper equipment or field method for the particular survey and terrain conditions • Insufficient horizontal and vertical control of suitable precision • Omission of some important topographic details

22. Global Positioning System (GPS) • Developed in early 1980’s by US Department of Defence • Made up of 26 satellites orbiting earth • 24 are functional and 2 spare • Each satellite is in a fixed position • Signals from at least 3 satellites are needed for accurate positioning • Receivers with high position accuracy are fairly expensive

23. Geographical Information System (GIS) • GIS are computer programs that allow users to store, retrieve, manipulate, analyze and display spatial data • GIS techniques are now being used in many fields, such as physics and medicine • GIS components • Hardware (computer) • Software • Data • Operator

24. GIS Data Structures • A GIS has two main data structures: vector and raster • Vector is made up of points, lines and polygons

25. GIS Data Structures • Raster or grid is made up of pixels on computer screen