Visualizing Shorelines WITH COASTAL VIGNETTES

CARTOGRAPHY Henri Saijos, May 23rd, 2014

By Category...

Using coastal vignette in the edge between the land and a body of water can help cartographer to develop a visual hierarchy for map. An important cartographic principle to provide a clear separation and focus either on land or the water. The general idea is use gradually fading color to mimic that in general water tends to get deeper when moving out of the shoreline. The resulting vignette provides visual illusion of the new dimension and adds professional style of your map design.

Traditional Vector Buffering

There are several different techniques that can be used to create a such effects. Relatively heavy raster based methods and various vector-based methods. Most of the methods need heavy processing and require some additional datasets to be created. We also may need to break the GIS data integrity and for example merge polygons before executing buffer creation. Finally user creates multiple ring buffers around the source polygon and adds a color ramp to display each ring with different color. With this approach when data or symbology is updated, we usually need to recreate the buffers and symbology. In this article we demonstrate how to create a coastal vignettes on the fly using new vector methods provided by Mapnor Cartographer.

Vector Buffering using Mapnor Cartographer

Mapnor Cartographer is intruducing new methods to create vignette effects with less processing. This will enable on the fly vignetting even with larger datasets and allow cartographers to easily investigate various buffer parameters and colors in final map product. Two parameters need to be considerer: Distance between the rings and the number of rings. To get smooth vignette, distance must be small enough and ring count should control the effect overall size. Finally the result is displayed in preview and a map using virtual color ramp with alpha blended colors.


Standard buffers with no merging (bufferd separately) vs. fluctuating buffers (always separately).

Coloring model is important to get smooth result. With traditional buffering, each buffer ring color must be specified separately and the last buffer farthest from the land must be set to same color used to show the rest of the water body. This would need accurate coloring model and changing the background color would need to change buffer ramp colors.

With Cartographer the coloring is done using alpha blending and overlapping buffered areas. It means that only the base color of the effect must be specified with an appropriate alpha value. The final color is then result of blending to underlying color and each buffer will multiply the color RGB values through the effect until the nearest buffer is almost saturated. Eg. when using optimal alpha value like 5-15 the last buffer farthest from the land gets automatically the color near the background, which then fades out to near effect color.

Each color component is calculated using standard alpha blending formula: [final color] = alpha * [effect color] + (1 - alpha) * [back color].

Buffers Effect

Buffers is a new method introduced by Mapnor Cartographer to create vignette effect outside a polygon sources. This effect is supporting merging, which means that there is no need to merge or alter source data in any way. Three edge methods are supported for versatile buffer creation: mitered, bevelled and rounded.

Buffers are created on the fly as a layer effect. There is no need to create any additional datasets or alter the data in any way.


Standard buffers with no merging (geometries bufferd separately) vs. merging.

Buffer Overlay Effect

Buffer Overlay is a new versatile method introduced by Mapnor Cartographer to create vignette effect inside a polygon sources. This effect is also supporting merging, which means that the source polygons can be tiled as long as the adjacent boundaries are intact. Whether to use outer buffer or inner overlay depends on the data and a desired result. For example coastal vignette can be achieved in both ways: Using a water body polygons with inner overlay or using a land polygons with outer buffer effect.


Inner ovarlays for land polygons and outer buffer for same polygons.

The coloring with this effect is done in reverse order compared to standard Buffers. The polygon main color and opacity is specifying the color near the outer edge like opaque white in example pictures below. The effect color with alpha value is then specifying the overlay fill to be added into internal buffers. The usable alpha values are around 0 and 40 to get valid fading effect. The result is smooth color ramp between the fill color and the effect color. Lining can be used to enhance the effect or to mimic contouring when true contours are not available. All lining parametes can be set separately.

Vignette created using inner overlay with water polygons

Vignette created using outer buffer with land polygons

Fluctuating Buffers Effect

Interesting alternative for traditional buffering is to use fluctuating buffers method. This, with additive alpha blending will add irregularity and fluctuation to effect geometry and color formations especially in narrow bays and straits. Fluctuating Buffers is also supporting line geometry, which can be a beneficial in cases when area polygons are not available but intact borders are available. One more benefit is ability to add effect only to part of the line and visualize narrow bays in different ways than open sea coast. (Through the line override effect).

Created effect geometry with fluctuating buffers is slightly different than with base buffer. While buffer produces a smooth vignette, fluctuating buffers is maintaining the geometric forms more precisely and adds multiple overlays to overlapping buffer regions.


Standard buffers with no merging (bufferd separately) vs. fluctuating buffers (always separately).

Using Variable Parameters

New methods supports variable parameters to enhence the effect. With variable width setting the buffers near shoreline are constructed closer together than buffers outer from shore. This could help to provide seamless and quality output with even less buffering steps.

By using lining variable dash setting the dash size through the linings can be controlled. It means that dash size is gradually decreased when moving outer from shoreline. With this setting the result is emulating the hand made line vignette that resembles the type of coastal and lacustrine vignettes commonly seen on old historical maps.


Static and variable width and lining dash.

Considerations

On the fly blended coastal vignette is without doubt a demanding operation and can slow down the map rendering with large and detailed GIS data. Anyhow, the new advanced algorithms will enable quality level effects even on the fly. This is providing cartographers a greatly enhanced flexibility and productivity in cartographic production. Try it yourself by contacting us and getting a free evaluation...

Copyright © 2014-2017 Mapnor Oy. All Rights Reserved.