Layers

I am beginning, I think, to understand the concept of layers when applied to maps. Initially a map appears to be a flat one-dimensional representation of a part of the world. But even the most basic map has a number of features - hills rivers, lakes, villages towns etc. And I guess it was when I first discovered Google Earth that I understood that you can take a digital map and then decide to overlay it, or not, with roads, points of interest, town names etc.

I remember listening to a talk at last year's AGI conference on fresh fruit deserts (as opposed to fresh fruit desserts) in Liverpool. In that instance a map of Liverpool was overlaid with those retail outlets which sold fresh fruit and vegetables. Because increasingly shopping is done at out of town supermarkets, many small shops in the inner city have stopped stocking fresh produce because they cannot guarantee to sell it before it deteriorates. So there are whole parts on the inner city where it is impossible to obtain fresh fruit and vegetables. Yet these are the poorest areas of the city and it is in these areas where many people do not have their own cars. So they cannot get to out of town supermarkets. So a whole swathe of the poorest people in Liverpool have no real access to fresh food. They are eating tinned food, not always by choice, by by necessity. That for me was an example of using mapping and combining it with data whose connection to maps was not immediately obvious, in order to highlight the problem in a way that raw data could not.

Local government has the opportunity to overlay maps of their area with a whole host of data, from bus routes to school catchment areas to health service provision to drainage etc. This video from YouTube shows this working in San Francisco.

So I presume that a lot of the GIS software being developed is allowing maps to be overlaid with useful data either for internal use of for proving information to the public. Add I can undertand that if this layered information is held digitally then it can be analysed and the spatial relationship of the data can be queried in a range of different ways for a range of different purposes.

Am I beginning to understand at least the basic concepts do you think? Let's hope so.