Employment of Projections and Thematic Base-Map Compilation SP 240 Cartography Alex Chaucer

Employment of Projections and Thematic Base-Map

Compilation

SP 240 CartographyAlex Chaucer

http://images.google.com/imgres?imgurl=http://employees.oneonta.edu/farberas/arth/Images/Ambassadors/globe.jpg&imgrefurl=http://employees.oneonta.edu/farberas/arth/ARTH214/terrest_globe.html&h=957&w=911&sz=574&tbnid=MspzxUMiDwAJ:&tbnh=146&tbnw=139&start=25&prev=/images%3Fq%3Dglobe%26start%3D20%26hl%3Den%26lr%3D%26sa%3DN

Spatial Information Technology

Center

Thematic Map Compilation

Map Compilation

The selection, assembly, and graphic presentation of all relevant information required for the preparation of a map. Such information may be derived from other maps and from other sources.



Center

Thematic Map Compilation

Thematic Map Compilationthe process of constructing a new, unique map for a specific purpose with information from base maps or thematic maps (or both).

This outside information comes from topographical maps, derived maps (large-scale) or small to medium-scale maps.

The USGS large-scale maps are used to produce smaller-scaled ones. The accuracy of derived maps is key, so finding a reliable source is very important.



Center

The Employment of Map ProjectionsThere are a few items to consider when deciding on a projection for a

thematic map.

1. Projection properties - need to be suitable for the current design problem.

2. Deformational patterns - All world projections cause some shape distortion, but a projection should result in the least amount of deformities possible and those that appear should not affect the map’s purpose.

3. Projection center - the projection should allow for the map to be centered on the location of the design problem.

4. Familiarity - A map needs to have both parallels and meridians that are familiar to the reader to ensure it is understood.

5. Cost - Any cartographer has to consider cost during a project so the work hours needed to complete a map help determine which projection is most affordable.



Center

World Projections

Mollweide Projections (Carl B. Mollweide) are used for mapping world distributions. This projection has curved meridians causing the lines at 90 to form a complete circle; one hemisphere is a full circle. The overall projection is an ellipse and the individual meridians are elliptical arcs. Distortion occurs mostly at the corners where the meridians and parallels meet. Since it has a good overall shape this is the projection to use if the distortion does not affect the map significantly.

http://www.colorado.edu/geography/gcraft/notes/mapproj/gif/mollweid.gif



Center

World Projections

Hammer Projection. The Hammer differs from the Mollweide Projection in that it has curved parallels and less distortion at the intersection of the meridians and parallels. The overall outline is the same as the Mollweide, but it is harder to construct due to the curved parallels with no true scale to match. The Hammer Projection is also good to use for mapping world distributions.

http://www.geometrie.tuwien.ac.at/karto/norm23.gif



Center

World Projections

The Boggs eumorphic Projection (Whittemore Boggs, 1929) is a combination of the sinusoidal and Mollweide Projections. One advantage is that it has more accurate shapes along the equator because it has equal linear scales. Visually it is easy to see the main difference of this projection because the world becomes pointed at the North and South Poles where the meridians converge.

http://geology.er.usgs.gov/eespteam/GISLab/Cyprus/cartographic_roots.htm



Center

Resolution Regarding the Use of Rectangular World Maps

"WHEREAS, the earth is round with a coordinate system composed entirely of circles, and WHEREAS, flat world maps are more useful than globe maps, but flattening the globe surface necessarily greatly changes the appearance of Earth's features and coordinate systems, and WHEREAS, world maps have a powerful and lasting effect on peoples' impressions of the shapes and sizes of lands and seas, their arrangement, and the nature of the coordinate system, and WHEREAS, frequently seeing a greatly distorted map tends to make it "look right," THEREFORE, we strongly urge book and map publishers, the media and government agencies to cease using rectangular world maps for general purposes or artistic displays. Such maps promote serious, erroneous conceptions by severely distorting large sections of the world, by showing the round Earth as having straight edges and sharp corners, by representing most distances and direct routes incorrectly, and by portraying the circular coordinate system as a squared grid. The most widely displayed rectangular world map is the Mercator (in fact a navigational diagram devised for nautical charts), but other rectangular world maps proposed as replacements for the Mercator also display a greatly distorted image of the spherical Earth."

http://en.wikipedia.org/wiki/Image:PetersMap.jpg

Gall-Peters Projection



Center

Projections for Mapping Continents

The Bonne Projection (Rigobert Bonne)

"is an equal-area conical projection, with a central meridian and the cone assumed tangent to a standard parallel. All parallels are concentric circles, with the center of the standard parallel the apex of the cone. The central meridian is divided true to scale. All parallels are drawn with their lengths true to scale, and each is divided truly. The meridians are drawn through the points of division along the parallels." (Dent, 1990)



Center

Mapping Large and Small Countries at Mid-Latitudes

For large and small countries at mid-latitudes either the Bonne, Lambert azimuthal equal-area or Albers equal-area Projection can be used.

A Lambert azimuthal equal-area Projection causes little shape distortion so it is a good choice for countries with symmetrical shapes. This projection is developed onto a plane that is tangent to the generating globe at one point. Any point can be used, but most often the North and South Poles are used. The azimuth of any point is correct in this projection so it useful for mapping information that has an important directional relationship to the central point of the map.



Center

Mapping Large and Small Countries at Mid-Latitudes

The Albers equal-area Projection is a conic projection with two standard parallels and has the lowest possible scale distortion for areas as large as the United States. This type of projection is good for areas with extended east-west length such as the U.S. The advantages of the Albers Projection are: a low 1.25% error in the map scale for a country the size of the U.S.; the meridians and parallels intersect at right angles; the conical shape is good for east-west lengths and for making section maps because the pieces will join together.



Center

Unique Solutions To The Employment of Projections

Today you might see•Oblique maps•Maps draped over globes



Center


The Gall-Peters Projection has created controversy in recent history for its unique representation. It may be a combination of Gall’s work in the 1880s and Peter’s Projection from 1972. The philosophy behind creating this projection was the thought that the Mercator projection is not accurate enough because of distorted area shapes and because Europe appears too large and dominant.





Center

Gall-Peters Projection vs. Mercator


Gall-Peters Projection Mercator Projection



Center

The Selection of Projections for Individual States and the State Plane Coordinate System

State Plane Coordinate Systemrectangular plane coordinate system applied to states;

Used especially by highway engineers, utility companies, andPlanners; grids labeled in feet and meters.

Uses 3 conformal projections1. Lambert conformal conic for states with long east-west dimensions2. Transverse Mercator for states with long north-south dimensions3. Oblique Mercator for portions of Alaska



Center

The Selection of Projections for Individual States and the State Plane Coordinate System



Center

Base Map Compilation

• Most base map compilation today takes place on a computer

• Issues related to generalization• Compilation sources• Preparing a base map for scanning• Copyright issues



Center

Compilation and GeneralizationCartographic Generalization

A central function in cartographic compilation; involves simplification, selection, and emphasis

Simplification is utilization of good judgment in the selection of detail when assembling a good base map, usually from preexisting computer map files.



Center

Compilation and Generalization

"Base map information serves to help readers orient the thematic information to a spatial or geographical frame of reference. The designer’s task is thus to select on those base map features that will help the reader in the context of the map’s purpose.“

Guidelines for Manual Base-Map Production

1. Map purpose2. Objective Evaluation3. Avoid Personal Bias4. Determine what Elements Typify the Area’s Character5. Uniformity



Center

Compilation and GeneralizationWhat is Compiled in a base-map?

Map purpose dictates the level of generalization.Think: what helps the map reader to orient themselves?

Commonly included:Basic Physical Features (coastlines, lakes, rivers, streams, mountains)Political Boundaries (Town, Village, City)Geographic Grid



Center

Compilation and Generalization

Line Generalization in Computer FilesNeed to have just the right amount. Too generalized can look childishToo detailed can look awkward



Center

Compilation Sources

Base map information has to come from other sources, most often previously made maps.

The USGS provides the largest percentage of maps for the U.S.

1:24,000 – topographic scale to 1:1,000,000



Center

Compilation Sources

GNIS (Geographic Names Information System) nearly two million geographic names with information and geographic coordinates of each.

For Mapping Foreign Lands:International Map of the World (USGS, 1:1,000,000 scale)Digital Chart of the World(NIMA, www.nima.mil)



Center

United States National Map Accuracy Standards

Map Accuracy – degree of conformance to established standards; has particular significance with relevance to maps at topographic scales but loses relevance when applied to thematic maps.



Center

Preparing a Base Map for Scanning

Reduction methods include "lifting" or tracing selected objects from one source onto a worksheet and making the worksheet match the map scale. This method is good to use for accuracy of locations. This allows you to only trace the important information for your new base map.

Common-scale methods compile information from various sources and put it into one worksheet. With this method you are able to gather information from different maps and put them all into one base map. Attention to scale is important because all of the different maps have to be set at one scale to end with an accurate final base map.

The simplest method, the one-to-one method is rarely useful. This method simply involves tracing features at one scale from the source map onto a new worksheet. It is not common for all base maps to be in the same scale you are working with.



Center

Copyright

There are rules governing the copyright of maps.

Exercise caution when using other’s source material.

There may be specific licensing agreements for map or other data files.


Documents

Employment of Projections and Thematic Base-Map Compilation SP 240 Cartography Alex Chaucer