Cartography and Geo-Visualization

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This section covers the basic definitions and development of cartography, the classification and types of maps, map scale, the enlargement and reduction of maps, and the uses of maps.

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Definitions • Cartography (ICA) is the art, science and technology of making and using maps.

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A map is a symbolised, generalised and scaled representation of geographic reality, showing selected features or characteristics, designed for use where spatial relationships matter. • Related terms: a plan is a large-scale representation of a small area in which curvature is neglected and the scale is effectively constant; a chart is a map designed for navigation (nautical or aeronautical); an atlas is a systematic collection of maps; a map series covers a region in uniform sheets at one scale. • Geo-visualization is the use of interactive, dynamic visual displays of geospatial data to explore, analyse, synthesise and present information — in MacEachren's cartography cube it lies at the 'private, high-interaction, exploration of unknowns' corner, while traditional map communication lies at the 'public, low-interaction, presentation of knowns' corner. • Cartographic abstraction proceeds by selection, classification, simplification and symbolisation; the map communication model describes the chain from reality through the cartographer's map to the user's mental image, with possible loss at every stage.

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Development of Cartography • Babylonian clay tablets (≈ 2300 BC);

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Greek scientific cartography — Eratosthenes measured the earth, and Ptolemy's Geographia (≈ 150 AD) introduced latitude, longitude and projections;

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Roman itineraries; medieval portolan charts and mappae mundi;

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Mercator's projection (1569) for navigation; national topographic surveys from the 18th century (Cassini in France, Ordnance Survey, the Great Trigonometrical Survey of India); thematic mapping in the 19th century (John Snow's cholera map, 1854); aerial photography and photogrammetric mapping in the 20th century; and from the 1960s computer-assisted cartography, GIS, digital map production, web mapping and geovisualization. • In Nepal, the Survey Department produced the national topographic base maps at 1:25 000 and 1:50 000 in the 1990s using aerial photography, and now maintains digital topographic and cadastral databases and web map services.

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Classification and Types of Maps Basis Classes Scale Large-scale (small denominator, much detail — cadastral plans 1:500–1:5 000, topographic 1:10 000–1:50 000); medium-scale (≈ 1:50 000–1:250 000); small-scale (smaller than ≈ 1:250 000 — atlas and wall maps).

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Thresholds vary between authorities Content / purpose General-reference (topographic) maps show many kinds of feature without emphasis; thematic maps show the distribution of one theme (geology, land use, population, rainfall); cadastral maps/plans show property boundaries; charts for navigation; special-purpose maps (tourist, road, hazard, utility) Data nature Qualitative (nominal — soil type, land use) and quantitative (population density, elevation) Form of production Analogue (printed) and digital (screen, web, interactive, 3-D) Other By projection, by dimensionality (2-D, 2.5-D, 3-D), by permanence, by medium Map Scale, Enlargement and Reduction • Scale may be expressed as a representative fraction (RF), in words ('one centimetre to one kilometre') or by a graphical (bar) scale, which remains valid after photographic reduction or paper shrinkage.

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On a map, scale strictly holds only at the standard line or point of the projection (6.2). • Enlargement and reduction: the linear factor is the ratio of the new to the old scale; areas change as the square of that factor (doubling the linear scale quadruples the area).

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Methods: the grid (square) method of copying square by square, the pantograph, similar-triangle and proportional dividers, photographic enlargement/reduction, and today simple digital scaling. • Cartographic consequence: changing scale is never a purely geometric operation — on reduction, symbols, line weights and lettering must be redesigned and the content must be generalized (6.4), or the map becomes illegible; on enlargement, no new detail or accuracy is created, and the enlarged map can mislead the user about its precision.

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Uses of Maps • Navigation and route finding; planning and administration (land use, infrastructure, boundaries, elections); engineering design and construction; resource management (forest, water, minerals, agriculture); disaster management (hazard, risk, damage and relief mapping — important in Nepal for earthquakes, landslides and floods); tourism and recreation; education and research; military use; legal use (cadastral maps as evidence of property); and as the base and framework for GIS analysis and decision making.

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This section covers the classification of map projections, map distortion and the scale factor, the choice of projection in national and international practice, and map sheet numbering, including the numbering of topographic base maps in Nepal.

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Projections and Their Classification • A map projection is a systematic transformation of the curved surface of the ellipsoid/sphere onto a plane.

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Because a curved surface cannot be flattened without deformation, every projection distorts one or more of shape (angles), area, distance and direction — the cartographer chooses which property to preserve. • By developable surface: azimuthal (planar), cylindrical and conical, plus pseudo-cylindrical, pseudo-conical and mathematical/compromise projections (Mollweide, Sinusoidal, Robinson, Winkel Tripel). • By aspect: normal (polar for azimuthal, equatorial for cylindrical), transverse and oblique.

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By contact: tangent (one standard line/point where the scale is true) or secant (two standard lines, spreading the distortion). • By preserved property: conformal (orthomorphic) — angles and local shape preserved (Mercator, Transverse Mercator, Lambert conformal conic, stereographic); equal-area (equivalent) — areas preserved (Albers, Lambert azimuthal equal-area, Mollweide); equidistant — true distances from a point or along certain lines; azimuthal (true direction) from the centre; and compromise, which preserves nothing exactly but looks balanced.

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Distortion and Scale Factor • The scale factor k at a point is the ratio of the local (actual) scale to the nominal (principal) scale: k = 1 on the standard line(s), less than 1 inside a secant band and greater than 1 outside it. • Tissot's indicatrix visualises the distortion at a point: an infinitesimal circle on the earth becomes an ellipse on the map — for a conformal projection it remains a circle (of varying size), and for an equal-area projection its area is unchanged (but its shape is distorted). • In UTM, k = 0.9996 at the central meridian, rises through 1 at about 180 km either side and reaches ≈ 1.0010 at the zone edge; in Nepal's MUTM, k = 0.9999 on the central meridian of each 3° zone.

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Survey computations must apply the scale factor to distances, the grid convergence between grid north and true north, and the (t − T) correction to directions in precise work.

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Choice of Projection • The choice depends on: the location, extent and shape of the area — polar regions suit azimuthal projections, mid-latitude areas extending east-west suit conic projections (Lambert conformal conic), and areas extending north-south suit transverse cylindrical projections (Transverse Mercator); the purpose — conformal for navigation, topographic mapping and survey computation, equal-area for statistical and thematic maps, compromise for world maps; the scale and the acceptable distortion; and national or international convention, which usually decides the matter in practice. • National practice:

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Nepal uses the Modified UTM (MUTM) with 3° zones (central meridians 81°, 84° and 87° E, k = 0.9999) for topographic and cadastral mapping, and UTM zones 44 and 45 for other products;

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India uses Lambert conformal conic and polyconic projections for its series; most countries adopt a conformal projection for their national grid.

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International practice:

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UTM/UPS with the MGRS grid reference system for military and general use, Web Mercator (EPSG:3857) for web map tiles, and equal-area or compromise projections for global thematic maps.

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Map Sheet Numbering • A sheet numbering (indexing) system gives every sheet of a map series a unique, systematic identifier derived from its geographic position, so that sheets can be ordered, stored and assembled. • International practice — the International Map of the World (IMW) 1:1 000 000: sheets of 6° of longitude × 4° of latitude; latitude bands are lettered A to V from the equator, longitude columns numbered 1 to 60 eastwards from 180°, prefixed N or S — for example NH-45.

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IMW sheets are subdivided systematically for the 1:500 000, 1:250 000 and 1:100 000 series; the MGRS gives an alphanumeric grid reference within UTM zones. • Survey of India practice: a 4° × 4° degree sheet numbered (e.g.

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72) is divided into 16 sheets lettered A–P for 1:250 000, each of those into 16 numbered 1–16 for 1:50 000, and each of those into four quadrants (NE, NW, SE, SW) for 1:25 000. • Nepal's topographic base maps: the country is covered by 1:25 000 sheets in the Terai and the middle hills and 1:50 000 sheets in the high mountains, on the MUTM/UTM grid with the Everest 1830 ellipsoid.

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The sheet number is built from the latitude and longitude of the degree block plus a sheet number within it (for example a number of the form 2785-xx, where 27 and 85 are the degrees of latitude and longitude); each 1° × 1° block is subdivided into the 15′ × 15′ sheets of the 1:50 000 series and the 7½′ × 7½′ sheets of the 1:25 000 series.

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(Verify the exact convention and subdivision from the current Survey Department index.)

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This section covers the principles and objectives of map design, map symbols, visual hierarchy, measurement scales, the graphic visual variables and their associations, and thematic map presentation.

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Principles and Objectives of Map Design • Design begins with the purpose of the map and its intended audience, the medium (print or screen), the scale and the data available.

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The objectives are clarity and legibility, an accurate and honest representation, and an attractive, balanced product. • Design principles: visual contrast (between features and background); figure-ground organisation (making the area of interest stand out, e.g., by a coloured land area against a plain sea); visual hierarchy (important elements attract attention first); balance of the elements about the visual centre (slightly above the geometric centre); harmony and unity of styles and colours; simplicity — nothing on the map that does not serve its purpose; and legibility at the intended viewing distance.

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Map Symbols • Symbols stand for real features.

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They are classified by dimension as point (well, temple, spot height), line (road, river, boundary, contour) and area (forest, lake, land parcel) symbols — and by their degree of abstraction as pictorial (mimetic), associative and geometric/abstract symbols. • Symbols may be qualitative (showing kind — a hue or shape) or quantitative (showing amount — a size or value).

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Proportional symbols scale the area of the symbol to the value; because people underestimate the size of large circles, apparent-magnitude (perceptual) scaling is sometimes used, or values are grouped into graduated symbols.

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Whatever is chosen, the legend must show the symbols exactly as drawn.

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Visual Hierarchy and Measurement Scales • Visual hierarchy is the organisation of the map so that the most important information is seen first and the base information recedes.

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It is created with size, lightness (value) contrast, colour saturation, detail, sharpness and position, reinforced by layering of the content; the intellectual hierarchy (what matters) should match the visual hierarchy (what is seen). • Measurement (data) scales — the key to choosing symbolisation: nominal (categories without order — land use classes), ordinal (ranked, without measured intervals — road classes, low/medium/high risk), interval (measured, with an arbitrary zero — temperature in °C) and ratio (measured, with a true zero, so ratios are meaningful — population, rainfall, area).

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Graphic Visual Variables Visual variable (Bertin) What it conveys best Position Location — the fundamental variable; also the most accurate for quantities (graphs) Size Quantitative differences (amount) — proportional/graduated symbols and line widths; strongly ordered and selective Shape Qualitative differences (nominal categories) — point symbols; it is associative but not ordered Value (lightness) Ordered data — the basis of choropleth shading; dark = more, light = less Colour hue Qualitative differences; hue has no inherent order, so it should not be used alone for magnitude Orientation Qualitative differences; also direction (arrows, wind, dip) Texture / grain (pattern spacing) Ordered and qualitative differences; substitute for value in black-and-white printing Modern additions Saturation, arrangement, crispness, resolution and transparency — plus the dynamic variables of animated maps (6.5) • Bertin described each variable by its perceptual properties — associative (categories seen as equal), selective (one class can be picked out at a glance), ordered (classes seen in rank order) and quantitative (ratios can be judged).

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Only size and position are quantitative; value and texture are ordered; hue, shape and orientation are selective/associative but not ordered — so matching the variable to the measurement scale of the data is the central rule of symbolisation.

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Thematic Map Presentation Thematic map type Use and rules Choropleth Areas shaded by value for enumeration units (districts, wards).

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Must use standardised data — rates, densities, percentages — never raw totals, because the areas differ in size; requires classification (6.6) and a sequential or diverging colour scheme Proportional / graduated symbol Symbol size proportional to the value at a point or for an area — suitable for absolute totals (population of towns, production) Dot density Each dot represents a fixed quantity; dots placed where the phenomenon occurs — shows distribution and density of absolute values; needs a stated dot value and careful dot size Isoline (isarithmic) Lines of equal value for a continuous surface — contours, isotherms, isohyets; includes isopleths for derived (density) surfaces Dasymetric Like a choropleth, but the boundaries follow the actual distribution (using ancillary data such as land cover), giving a more truthful picture Cartogram Area or distance distorted in proportion to the value (value-by-area) — striking but geographically distorted Flow map Line width proportional to the volume of movement between places (migration, trade, traffic) Others Heat/density surfaces, bivariate and multivariate maps, animated and interactive thematic displays

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This section covers the definition, types and guidelines of generalization, typographic grammar and guidelines, toponymy, colour theory, colour guidelines and colour models.

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Generalization • Cartographic generalization is the selection and simplified representation of detail appropriate to the scale and purpose of the map.

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It is needed because the available space shrinks with the square of the scale reduction while the features do not, and because too much detail destroys legibility and the message. • Types: model (statistical/database) generalization — reducing the detail of the data model itself, independent of graphics; and cartographic generalization — adjusting the graphic representation for a particular scale and product. • Operators: selection/elimination (which features to keep), simplification (fewer points in a line), smoothing, aggregation/amalgamation (merging nearby buildings into a built-up area), merging, collapse (an area symbol becomes a point or line — a town becomes a dot), typification (representing a pattern with fewer typical symbols), exaggeration (a road or river drawn wider than scale so that it remains visible), displacement (shifting symbols apart to avoid coalescence), enhancement, classification and symbolisation. • Töpfer's radical law estimates how many features should be retained: nf = na √(Sa/Sf), where na is the number on the source map at scale denominator Sa and nf the number on the derived map at Sf. • Guidelines: preserve the geographic character and relative importance of features; keep relative positions and topology correct; avoid overlap and coalescence of symbols; maintain a consistent degree of generalization over the whole sheet; and never generalize away information essential to the map's purpose.

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Typography and Toponymy • Lettering is a graphic element like any other: type carries meaning through its size, weight, style, case, colour and spacing.

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Terms: typeface/font family, serif (with terminal strokes — traditional, for cultural/administrative names) and sans-serif (clean, legible at small sizes), roman, italic and bold styles, size in points (1 pt ≈ 0.353 mm), leading (line spacing), kerning/tracking (letter spacing) and halo/mask (a light outline placed behind the text so that it stays legible over busy detail). • Typographic grammar (conventions): italics for hydrographic features (rivers, lakes, seas); upper case and larger type for larger or more important features (countries, provinces, large cities); size and weight graded to show the hierarchy of settlements; letter-spaced names to cover the extent of an area feature; colour matched to the feature class (blue for water, green for vegetation). • Placement rules (Imhof): names must be legible, unambiguous and clearly associated with their feature, and must not obscure other detail.

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Point features — the preferred position is to the upper right of the symbol, then upper left, lower right, lower left; line features — the name follows the line, curved and repeated at intervals, placed above the line and read left to right; area features — the name is placed inside, spread along the axis of the area, or outside with a leader if it does not fit.

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Names must not cross other names or important lines, and should be kept horizontal or aligned with the feature rather than upside down. • Toponymy is the study and standardisation of place names — their collection in the field, correct spelling and romanisation/transliteration, treatment of generic and specific parts, official approval by a national names authority (in Nepal the Survey Department and the nomenclature committee work with official administrative names), and publication in a gazetteer; the UN Group of Experts on Geographical Names (UNGEGN) provides international guidance.

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Colour Theory and Models • Dimensions of colour: hue (the colour itself — red, green, blue), value/lightness (light to dark) and saturation/chroma (intensity or purity). • Colour models:

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RGB — additive, mixing light, used for screens (red + green + blue = white);

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CMY(K) — subtractive, mixing inks, used for printing (cyan + magenta + yellow, with black added for depth and text);

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HSV/HSL — intuitive for design;

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Munsell and CIELAB — perceptually ordered systems used for specification and conversion.

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Screen and print colours must be managed (ICC profiles) because their gamuts differ. • Colour schemes for data: qualitative (distinct hues of similar lightness for nominal categories); sequential (one hue, light to dark, for ordered data — dark means more); diverging (two contrasting hues with a neutral critical midpoint, for data departing from a mean or zero).

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ColorBrewer provides tested schemes. • Guidelines: limit the number of classes (about 5–7); ensure sufficient lightness contrast between adjacent classes; respect conventions (blue for water, green for forest/vegetation, brown for contours and relief, red for main roads and built-up areas, yellow for agriculture); be aware of simultaneous contrast (a colour looks different against different surroundings); design for colour vision deficiency (about 8% of men have red-green deficiency — avoid red/green pairs alone and add differences in lightness or pattern); and check the appearance in both print and screen.

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This section covers the introduction to digital cartography, the raster and vector data models, the steps of digital map making, conventional versus digital cartography, the digital landscape model and digital cartographic model, client-server architecture, OGC standards, and dynamic maps and dynamic visual variables.

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Digital Cartography and Data Models • Digital cartography is the production, storage, manipulation and display of maps by computer, in which the map is derived from a spatial database rather than drawn once and for all.

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Its advantages are easy editing and updating, the ability to change scale, projection and symbolisation, output to many media (print, PDF, screen, web service), automation, integration with analysis, and archiving; its challenges are data quality and cost, the difficulty of automating generalization, and the need for software skills and standards.

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Raster model Vector model The area is divided into a grid of cells (pixels), each with a value; location is implicit in the row/column Features are stored as points, lines and polygons defined by coordinates, with topology and attributes Simple structure; ideal for continuous surfaces and imagery (DEM, satellite images, scanned maps) Compact for discrete features; precise boundaries; ideal for cadastral parcels, networks and administrative units Large data volume; resolution-limited boundaries; easy overlay and map algebra Complex overlay processing; supports network and topological analysis; scales without loss of definition Conversion: rasterisation of vector data Conversion: vectorisation of scanned raster maps Steps of Digital Map Making • (1) Planning and specification — purpose, scale, content, datum and projection, symbol set.

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(2) Data acquisition — field survey/GNSS, photogrammetry, remote sensing, LiDAR, or existing maps and registers.

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(3) Digitising or scanning of existing maps with georeferencing.

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(4) Editing, cleaning and topology building (closing polygons, removing slivers and overshoots).

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(5) Attribute entry and database structuring.

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(6) Generalization and symbolisation for the target scale.

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(7) Layout and design with the map elements (6.6).

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(8) Quality control — positional, attribute and logical consistency checks.

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(9) Output and dissemination — printing, PDF, web services — with metadata and archiving.

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Conventional cartography Digital cartography Manual drawing/scribing on film or paper Database-driven, drawn by software Editing means re-drawing; costly corrections Easy editing, versioning and updating One product at one scale and projection Many products, scales, projections and media from one database Reproduction by photomechanical processes Output to print, PDF, web tiles or services Skills: draughtsmanship Skills:

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GIS/database, design and programming DLM and DCM • A Digital Landscape Model (DLM) is an object-oriented model of the real landscape — the geometry, topology and semantics (attributes) of real features, stored independently of any graphic representation, and maintained at defined levels of detail (Base DLM, DLM50, DLM250…). • A Digital Cartographic Model (DCM) is the graphic, symbolised representation derived from the DLM for a particular product, scale and medium — with symbols, displaced features, lettering and layout. • Two kinds of generalization follow: model generalization (DLM → DLM), which reduces the content of the database itself for a smaller scale, and cartographic generalization (DLM → DCM), which adapts it graphically for display.

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Keeping the two separate is what allows one database to serve many map products.

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Web Cartography, Client-Server Architecture and OGC Standards • In a client-server architecture, the client (a browser or mobile app) requests data or map images from a server (web server + map server such as GeoServer, MapServer or ArcGIS Server + a spatial database).

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A thin client only displays what the server renders; a thick (fat) client receives the data and renders and analyses them locally.

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Performance comes from pre-rendered tiles and caching, and from scale-dependent content. • OGC (Open Geospatial Consortium) standards make services interoperable:

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WMS (Web Map Service — rendered map images), WMTS (tiled maps), WFS (Web Feature Service — the vector features themselves, in GML), WCS (Web Coverage Service — raster/coverage data), CSW (Catalogue Service for metadata search), SLD/SE (styling), WPS (processing), and formats such as GML, KML and GeoPackage, now being modernised as the OGC API family.

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They underpin spatial data infrastructures (Chapter 7). • Dynamic maps and dynamic visual variables: animated and interactive maps add the temporal dimension.

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The dynamic visual variables (DiBiase, MacEachren) are duration, rate of change, order, display date (moment), frequency and synchronisation, used in addition to the static variables of 6.3.

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Interactivity — pan and zoom, layer switching, query and identify, filtering, linked views and brushing, animation control — turns the map from a finished statement into a tool for exploration, which is the essence of geovisualization.

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This section covers data classification techniques, map layout prerequisites, elements and balance, an introduction to map reproduction, contact photography, thickening and thinning, plate making and map printing.

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Data Classification Techniques Method Description and use Equal interval The range is divided into classes of equal width — simple and easy to read, but classes may be empty or overloaded if the data are skewed Quantile Each class contains the same number of observations — good for ranking and for a balanced-looking map, but it may place very similar values in different classes Natural breaks (Jenks optimisation) Class limits are set where natural gaps occur, minimising within-class variance — represents the data structure best, but the limits are awkward and maps are hard to compare Standard deviation Classes defined by distance from the mean — shows departures from the average, and suits a diverging colour scheme Arithmetic/geometric progression, nested means, manual Used for strongly skewed data or to impose meaningful limits (e.g., planning thresholds) • Rules: use about 4–7 classes (more cannot be distinguished visually); class limits must not overlap and must leave no gaps; state the method in the legend; and remember that the same data classified differently can produce very different maps — an ethical as well as a technical matter.

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Unclassed choropleth maps avoid the problem by mapping the value continuously.

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Map Layout — Prerequisites, Elements and Balance • Prerequisites: knowing the purpose, audience, medium, format/sheet size, scale and the content to be shown. • Elements: the map body (the mapped area); title (and subtitle) saying what, where and when; legend explaining every symbol used; scale (bar and RF); north arrow/orientation; grid or graticule with coordinate labels; projection and datum note; inset/locator maps; source, date of data and date of publication; author/producing agency and copyright; sheet number and adjoining-sheet diagram for a series; neatline and border; and any explanatory text or graphs. • Balance: the elements are arranged around the visual centre, which lies slightly above the geometric centre of the sheet; each element has a visual weight (larger, darker, more complex items weigh more) and a visual direction, and these must be distributed so that the layout does not feel lopsided.

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Related ideas: alignment on an underlying grid, generous but controlled white space, consistent margins, and a clear figure-ground relationship between the mapped area and the surround.

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Map Reproduction • Reproduction is the process of making many copies of the compiled map.

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In the traditional photomechanical workflow the drawn or scribed original was photographed and converted into film negatives or positives — one for each printing colour (colour separation); continuous tones and percentage tints were produced by screening (halftone dots); registration marks ensured that the separations printed exactly on top of one another; and proofs were checked before printing. • Contact photography: film is exposed in a vacuum frame in direct contact with the original (rather than through a camera lens), using a point light source — giving an exact same-size copy with maximum sharpness.

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It is used to make positives from negatives (and vice versa), to combine separations, and to produce duplicates of the drawing. • Thickening and thinning (spreads and chokes): by slightly diffusing the light or separating the film from the original during contact exposure, line and symbol edges can be made marginally thicker (spread) or thinner (choke).

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This is used to control line weight and to provide trapping — a small overlap between adjacent colours so that a tiny misregistration does not leave a white gap. • Plate making: the image is transferred to a presensitised aluminium printing plate by exposure to ultraviolet light through the film (positive-working or negative-working plates) and development, which leaves the image area oleophilic (ink-receptive) and the non-image area hydrophilic (water-receptive).

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In the modern workflow, computer-to-plate (CTP) imaging writes the plate directly from the digital file with a laser, eliminating film altogether; digital presses need no plate at all.

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Map Printing • Offset lithography is the standard process for map printing: it works on the mutual repulsion of grease and water — the damping system wets the non-image areas, the ink adheres only to the image areas, and the inked image is transferred (offset) from the plate to a rubber blanket cylinder and from there to the paper, which gives a sharp impression on many paper types. • Flat-bed printing uses a flat plate and is slow — suited to proofs, small runs and special materials; rotary (web or sheet-fed) offset mounts the plate on a cylinder and prints at high speed in multiple colours, and is used for large runs of map sheets and atlases. • Other processes: screen printing (for thick inks and unusual materials), gravure (very long runs), and digital printing (inkjet and toner, including large-format plotters), which needs no plates and is now the normal choice for short runs, proofs, on-demand and personalised maps. • Production considerations: paper type and weight, ink and colour management (ICC profiles, proofing), resolution (dpi) and screen ruling (lpi), accurate registration of the colours, drying, folding, trimming and binding, and the preservation of the digital master for future revisions.