Jeffery S. Nighbert

Using ArcGIS to Apply Textures and Materials to Relief Backdrops in Cartographic Presentations

Shaded or painted relief backdrops add tremendous visual interest and value to cartographic products. The addition of relief backdrops to maps has proven an effective technique for portraying realistic landscapes and geographical situations and it is widely practiced in cartography today. However, the beautifully smoothed and colored shaded relief surfaces commonly seen as backdrops on many maps often do not reveal the true character of the ground being shown. By enhancing painted or shaded relief with textures and materials, more realistic information can be displayed and therefore provides map users a better sense of the geographical situation present in the map. The information required to develop these geographic textures and materials can be derived from a number of widely available digital sources, including digital aerial photography, satellite imagery and other GIS thematic data. Incorporation of this additional information is desirable and possible while still maintaining visual balance and readability. This presentation will discuss the concepts and philosophy behind the use of geographic textures and materials. It will also provide a step-by-step application example showing how landscape based textures and materials can be applied to cartographic backdrops using ArcGIS to create a dramatic, interesting and informational cartographic presentation.

INTRODUCTION

Traditional thematic maps and plats offer little to let map users picture the true geographic character of the landscape shown, that is, the actual texture, material and pattern of the land's covering. The myriad lines and annotations on these products are just not concerned with presenting complex and important landscape characteristics such as terrain, land cover or land use. Yet, to remedy some shortcomings, cartographers have developed a number of techniques for terrain and landscape portrayal.The most widely used of these techniques is shaded relief or hill shading. In its most basic form, the term Shaded relief usually applies specifically to gray scale image which illustrates how the sun might shade the land given a constant solar azimuth and altitude. This gray scale image is incorporated as a backdrop image in the cartographic presentation. This technique tends to solve the basic problem of providing a geographic context for locating planimetric features, but has limited utility because it lacks the advantages of using color and texture.

Improvements in mapping software, computer graphics and printing technology now allow thematic and mapping and platting to easily take advantage of portraying underlying terrain features colorized shaded relief. This particular brand of cartographic presentation is called painted relief. Displaying thematic map information as painted relief has been an effective and popular cartographic method. It is practiced worldwide among production cartographers as well as the ever-growing population of Geographic Information Systems (GIS) users and countless beautiful, interesting, and informational maps are created using painted relief techniques. Yet, shaded relief, and even painted relief techniques do not address or include landscape patterns and provide no information about the actual materials covering the ground. The hill shaded terrain image generated from digital elevation information would not include important landscape patterns such as urbanization, farming, forestry, and many other landscape processes, nor the covering of the terrain; (ie Is the land cover material a forest, sand dunes, rocks, or snow?). Colorizing a theme's distribution and draping it on a relief model does nothing to address the actual land cover texture nor does it imply material. Indeed the shaded and painted relief image is generated from a statistical elevation model of the ground and it is unnaturally smooth and devoid of detail. This missing detail, in today's world, provides important insight into the nature and geography of an area. Depending on the purpose of the map, land cover patterns, textures and materials should be included in the cartographic presentations.

Many cartographers have sought raw image sources such as aerial photography and satellite imagery to show land cover patterns and textures in their presentations. But the raw image, even when ghosted for map clarity is essentially an information overload situation. In its uninterpreted form, raw imagery suffers from a number of problems: 1) relief inversion: hills may look like valleys, valleys may look like ridges; 2) features obscured due to shadows; 3) too much information shown: aerial images display everything--including unimportant items; 4) no visual hierarchy: unimportant items are shown on the same visual level as highly important items; 5) temporal problems: images get out of date; and finally 6) lack of control over what is shown: the role of the cartographer is to design and control information being presented, so the use of raw imagery as a source for geographic textures and materials must be made on a very selective basis.

On the other hand, aerial photography and satellite imagery, when used as a basis for a properly interpreted land cover map, can be a excellent source for mapping geographic textures and materials, since a good land cover map provide important information about the patterns, textures and materials of the lands's cover. It can provide the type of information needed to enhance painted relief techniques to a level where geographic textures and materials can be easily included in the cartographic backdrop without interfering with map readability.

This paper presents a single example which illustrates how to apply land cover textures and materials derived from satellite imagery to a painted relief cartographic backdrop. The study area is the Three Sisters Region of Central Oregon. This area was selected to demonstrate this technique because it embodies a wide range of land cover types that are typical of lands managed for multiple use by the Bureau of Land Management. Data sources for the project include 10 meter digital elevation models, a simplified land cover map derived from Landsat TM data, roads, streams, boundaries and geographic names were extracted from BLM GIS databases at the Oregon State Office. Esri's ArcMap product was used as a display tool, while the material and texture assignment was performed in the ArcGRID system utilitizing and Arc Macro Language (AML) program.

Step 1. Building materials,textures and patterns

For this demonstration, a simple land cover classification was performed using Landsat TM satellite information of the Three Sisters Region of Central Oregon. Seven land cover categories were mapped for the area: Water, Snow, Barren, Grass;, Shrub, and Lava. Simplicity was maintained for this demonstration. In actual practice more elaborate schemes would probably be used. The graphic below shows only a small portion of the entire study area since space is limited in this form.

Figure 1. Small portion of larger land cover category map of the Three Sisters Region, Oregon

To develop and build materials, textures and patterns, each land cover category must be evaluated for a number of characteristics: Color, texture, and reaction to light. Since land cover categories are generally an accumulation of many similar materials and textures, it may be a judgment call as to describing their appearance. The color of a class is fairly obvious. Texture can be presented in terms of the range of heights of individual objects that belong to that land cover category, while the reaction to light may vary from reflective surfaces such as snow and water to diffuse and absorbing surfaces such as forest stands. Below is a simple table used to guide the development of an AML program used to build a texture and material map for the area:

Table 1.Material comparison table.

These values were translated into a AML program which operates in the ArcGRID system. (Shown Below.) It uses the IF and NORMAL Grid functionality. The program establishes different textures for each material by evaluating values created using the NORMAL command, then setting a texture height for pixels meeting that criteria. For example, lava has values of 7 and 8 in the land cover map; where this is true and the normal_random noise map is > ; 15, set the output pixel equal to 70. This creates a very rough irregular surface pattern.

Roads and rivers are also incorporated into the product from vector sources, since they were not mapped in the land cover classification.

if (land_cover ge 9)

texture_elevation = merge(rivers * -10,roads_1 * 10,texture1)

Figure 2. AML program for setting texture, light reaction for each material in a land cover map

The program runs quickly and creates essentially and “elevation of texture” grid. It is shown below in shaded relief form so the final textures are more apparent.

Figure 3. Results of the texturizing AML program. (Results shown in shaded relief form.)

The image below shows how the land cover category color looks after it has been texturized.

Figure 4. Texturized Land Cover Categories.

The final step in the program sequence is to integrate the texture elevation information with the terrain elevation data. This is performed through the HILLSHADE command in ArcGRID. The command used is shown below:

hill_tex = hillshade((texture_elevation * .25) + terrain_elevation * 3.2,345,65)

The image below is the result of the above command and gives a better idea of the materials, textures and patterns of this landscape!

Figure 5. Final texturized terrain grid after integration of texture and terrain elevation and HILLSHADE.

2. Final Display and Mapping in ArcGIS

Since ArcGIS cartographic display capability supports data transparency, the final texturized terrain and the land cover grids are loaded into ArcMap. The Land cover map is assigned its colors and overlain on the texturized terrain. The image below shows the results of this process.

Figure 6. Final Texturized land cover materials and cartographic backdrop.

Figure 7. Larger area view of texturized land cover materials and cartographic backdrop.

Figure 8. Final Map Image of Three Sisters Region, Oregon.

CONCLUSIONS

The above example demonstrates one method of applying materials and texture to cartographic backdrops.  It illustrates that new technology provides cartographers options for creating richer and more interesting cartographic products. With this technology, more realistic and informational maps can be designed, more complex geography can be communicated and maps can be of better service to everyone.

Author Information:

Jeffery S. Nighbert
Bureau of Land Management
Oregon State Office 955.2
1515 SW 5th Avenue Portland, Oregon 97201
Phone:(503) 808-6399 Fax: (503) 952-6419
Email: jnighber@or.blm.gov

Bios:

Jeffery S. Nighbert has been a geographer with the Bureau of Land Management for over 20 years and is currently the Senior Technical Specialist for Geographic Information Systems (GIS) at the Oregon State Office, located in Portland, Oregon. He has extensive experience in GIS and holds a M.A. in Geography from University of New Mexico.