[Carto] Overview diagram - high quality maps and memory cost

Thu Aug 27 14:27:57 EDT 2009

Dear all

The best method for checking if this diagram is ok is try to clarify the aims of this project. In other words what does mean high quality, high resolution large format printing in cartography.

High resolution printing can be summarize as follows

resolution in dpi

300 dpi. Good resolution for photos and small and report maps. No so good for printing vector data

600 dpi. Nice resolution for photos, vector have better looking and forms can be better appreciation. Colors look brighter.

1200 dpi. High quality maps. Production maps, near printing shops resolution ( sorry but I don not how translate <lang=es>"imprenta"</lang=es> ) .

2400 dpi ???

Large format printing expressed in page size standards

A4. Very common page size. Most of the users need maps at A4 pagesize. Good size for reports and no so elaborated maps

A3. Good size for people who needs maps in the field. On site surveying. Very easy to handle in field work

A2. I don have experience with this map size

A1. Typical scholarship map size. A map that a lot of people wants to put in a wall

A0. Most of production maps belong to this category. Topographical, geological, etc.

Larger sizes Continental Maps, World Maps, Instructional maps, Poster Like maps, special projects maps, etc.

Quality Maps
There are too many issues related to what cartographers think what it is a high quality map but anyway let's first start with color.
A cartographic system must be capable of make printings using CMYK.

What I tried to explain putting resolution, page size and colors in table?. When I tried to introduce all of you in a very big problem. That is memory cost vs map quality.

Memory cost is a big issue in cartographic map production system and it put several constraints on:

Data Input
Data Processing
Data Output

Data Input
Let's start with raster data. I tried summarize constraints in few statements:
"Good quality raster maps need a source of data where pixel size at given map scale is the same of output resolution".
"If that condition can not be respected at least can be produced a new image with a zoom of 3x where the data left are interpolated"
"Compressed images can only be used in those cases where compressing methods do not produce artifacts"
"Use anyone of those two last methods if quality is not your objective"

I think those statements put a clear constraint about the use of WMS as a source of data, specially in high quality maps and also a big constraint about networks.

Data Processing
Difficulties related to manipulate high amount of data, mantain organized them, and moving (zoom out, in, pan) the objects in the screen.

Data Output
Print maps is a very difficult issue, especially due to what you see in you screen will not be the same you look in the paper. That is a problem of a specialist with universitary degree in digital printing. But anyway what we can tell is memory cost is also a big issue when people want print a map.

All the data edited and manipulated during the data processing step must be rasterized. It is usually rasterized to the output resolution using CMYK color model (32 bits). Try to remeber at what page sizes people want to print and what does means in terms of memory cost and data processing (we need to make some calculations).

A probable solution for memory cost in the Data Ouput step:
Create a high quality postscript file and leave the problem to others. That is what we did.

Gabriel Asato
Unidad Sensores Remotos y SIG
Servicio Geológico Minero Argentino
(SEGEMAR)
Av. Julio A. Roca 651 p 8 of 1
Cdad. Autónoma de Buenos Aires
ARGENTINA

tel 54-11-4349-3158/26
fax 54-11-4349-3287

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