Asian Surveying & Mapping
Breaking News
Chinese launch startup’s rocket fails during satellite launch
The Chinese launch company Galactic Energy suffered its first...
First Hong Kong-made satellite set to launch in November from Guangdong province, company reveals
The first Hong Kong-made satellite is set to be...
China launches Yaogan 39 remote sensing satellite
China launched a Long March 2D carrier rocket on...
Saudi Arabia publishes maps with new names for ceded islands
A new map published by Saudi Arabia’s General Authority...
US, Saudi Arabia conclude region’s largest-ever counter-UAS exercise
The US and Saudi Arabia conducted the largest-ever counter-UAS exercise...
Study improves accuracy of planted forest locations in East Asia
An international team led by Purdue University scientists has...
Iran, Russia Working On Joint Research Spacecraft
In an interview with Tasnim, the president of the...
France, Bangladesh sign deal to provide loans, satellite technology during Macron’s visit to Dhaka
French President Emmanuel Macron witnessed the signature of a...
Iran, Russia Working on Joint Research Spacecraft
TEHRAN (Tasnim) – Top universities from Iran and Russia...
India, Vietnam, Malaysia, Philippines and Taiwan reject China’s new ‘controversial’ map, release statements
China continues to receive brute criticism from countries that...
projection-albersequal

In a perfectly (flat) world, GIS buffering would assume a distance from a central point and draw a circle around that point of equal distance until it closes. It would look like a pie. The results would be accurate and one could roll up the paper and take it anywhere in the world, roll it out, and show it to clapping fans.

The problem is – the world is not flat. Datums matter. The concept of drawing that same circle on the world as we know it today gives rise to conflicts in positional accuracy and precision. This happens due to the fact that the world is not just unround, but it is very elongated elliptical shaped. In fact, recently released gravity data for the world and a new model describe the world more like an apple. That’s another story – let’s get back to the datums.

What really prompted this entry is the excellent article by Drew Flater and the Esri Geoprocessing Development Team (noted below). That team showed that if one uses a GIS software to buffer over wide areas, then datums ultimately play a more important role. Suddenly that nice circular buffer bends, twists and takes on a different shape, extending to conform with the existing datum (see the article pictures).

My guess is that many of us forget these quirks as they happen at times, reminded only when we see them in maps and other cartographic products that depend upon physical properties of the earth. In the case of the recent Japan Earthquake event it has particular significance.

As the buffer or so called radiation impacted area increases in size and is displayed using a map, then the significance of the datum begins to play a greater role. Depending on the size of the buffer, it may take on different meaning. Once we start talking about a few thousand kilometers or so in terms of radiative effects, then questions relating to distances begin to change as displayed in buffered computations.

It has been reported that the Japan land base was moved up to 25 meters in places due to the earthquake. In other places the land has shifted downward, causing the recent flooding we have witnessed, as heights decreased. It is important to understand that mapping and geospatial technologies consider the physical shape of the earth when operating. Accordingly, as seismic activity and other events occur, our solutions can be impacted.

References

Canadian Spatial Reference System (CSRS) High Precision Datum

SLA Coordinated Cadastre

Mean Sea Level, GPS, and the Geoid

Understanding Geodesic Buffering