GIS & OSM Basics

Home

GIS & EPSG

How map can be presented

In present days, map can be presented in browser via js client easyly, with support from map server. Based on client framework like leaflet or openlayers, tiled map pictures can be easily presented.

Map tiles are acturally pictures servered by a map server. The OSM is a good example. The service and data are free.

Here is the quickstart from openlayers with OSM tiles support.

If you are an experienced programmer, the above massage is enough for you to ba a "GIS Programmer", if such a profecient really exists.

But from the day you decide to do something about GIS, you need to know more about geography data itself. There are 2 things you need to keep in mind:

And here is the 3rd advice, only for Chinese programmers:

I'v got requests asking me showing geologicall locations marked from different map services. At first sight it's simple.
But here comes the radiculous part: locations are not considered correct compare to the orignal marks even when the really long-lat is known. Because you just don't show the loaction the same with some popular map service, basee on the map services in China.

It's often asked by clients that you must not show objects' locations with displacement from the "true" longitude and latitude. The resultes is that marks from different system won't displaced in the same way.
But why displacement is needed? For security!
You shouldn't doubt which enemy is so stupid that will collect data like this, it's not job of a programmer.

I must be appreciating that they don't asked anymore after I asked what the referencing measurement they used.

About EPSG, WSG84 & Mercato Projection

EPSG 4326 & CRS 80 (Xi'an 80)

References

OSM

GIS

Tools & Resources