Developing map area

[Hamid Ramazani]

Hi,

I have an osm file (from open street map), and need to extract highways (main streets generally); I have almost done this step by using related tools and docs on the open street map site.

The second step which I don't know how to do is:

I have draw areas adjacent to highways on the map, and divide them to equal areas.

For example I might end up with few thousand equal areas on a map for a simple city.

I don't know how to do that. Please help.

I'm new to gis and geotrellis.

Thanks a lot in advance.

[Robert Cheetham]

Hamid,

Thanks for you interest in GeoTrellis.  I'm having trouble picture the desired outcome for your task.  It sounds like you may be trying to perform a Euclidean Allocation operation in which each location in a city is assigned to the nearest street segment (or main street segment).  In this case, in a city with blocks of generally similar size and an orthogonal street grid, you might get areas of approximately equal size but they won't really be equal.  Is this your objective or am I missing something?

Regards,

Robert

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[Hamid Ramazani]

Robert,

Please note that I'm a software developer, and I have almost now idea about GIS, despite the fact that I really really like this area of study. I'll read few books about it, but I don't have that much time now.

This is what I have done:

I remove almost any feature in the map, and only keep highways. It means I have an osm XML file that contains only information about highways in the city.

This is what I want to do in plain English (not gis or software ...)

Alongside each highway I consider a width of 30 meters for example. Know I have a very long area with the width of 30 meters in one side of the highway, and same on the other side of they highway. They are separate areas.

Now, I need to divide each big area to small areas, for example each 50 meters long, so end up having a lot of 30*50 meter areas. I don't need them to be exactly equal, almost equal suffices.

Now I need to add some points, etc. to each divided area, and may need to monitor them and give overall maps about them, which geotrellis is great at doing that.

Now what can I do? Please give me step by step advise, since I'm a little unfamiliar in this area. If you think some documents, books, or resources will help me, please name them.

Thanks a lot in advance.

[Robert Cheetham]

Hamid,

Thanks.  This is really helpful.  I think I can picture what you are aiming for.  If I were to translate this to a sequence of operations, it might be something along the following lines:

 * Select a series of road segments (lines or polylines)

 * For each road segment, form a polygon that is constructed from a 30m offset on either side of the road segment

 * Split this polygon with the road segment to create two polygons for each road segment, representing a "blockface"

 * Split each blockface polygon into 50m sections

If I'm understanding you correctly, I do not think GeoTrellis is the right solution.  GeoTrellis is primarily a raster data processing framework (raster data is gridded data organized arrays of cells, like imagery, elevation and similar data) that is able to process large data sets rapidly by distributing the processing across multiple machines.

I think you might take a look at a couple of other spatial data processing toolkits that could likely be applied to help you achieve your objective:

 * PostGIS - http://postgis.org/ - a geospatial extension of the PostgreSQL database that has a very powerful set of vector processing functions that extend SQL for this type of processing.  The general workflow is to load a shapefile as a database table (and there is support for OSM data as well) and then use the geospatial SQL extensions to select or modify the data.

 * Quantum GIS (QGIS) - http://www.qgis.org/ - QGIS is a desktop GIS visualization and processing software.  It includes a number of functions that can be extended using Python.  QGIS also includes support for connecting directly to a PostGIS database.

 * ArcGIS - it's not open source, but a combination of ArcGIS Desktop (http://desktop.arcgis.com/) and ET GeoWizards (http://www.ian-ko.com/ET_GeoWizards/) would likely also enable you to work through this process as well.

Regards,

Robert

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