03/05/2013

Basic Statistics

SQL squery
Statistic result base on filtered output
Same result from a filtered layer
Statistics Am

Pernahkah anda memikir bagaimana untuk mendapatkan 'sum of' sesuatu dari peta, contohnya, kawasan keseluruhan fitur 'hutan'? Sekiranya anda menjangka ianya boleh dihasil melalui SQL query, fikir sekali lagi kerana Search Query Builder tidak dapat menghasilkan apa yang nak dicari. Gunakan alat sewajar untuk kerja yang spesifik kata  mekanik kereta saya dan perkara seperti sum of, mean, median dan mode terletak dalam alam statistics, maka, alat paling sesuai adalah modul Basic Statistics dibawah Vector/Analysis tools. Pada ujian pertama, Search Query Builder diguna untuk membuat carian yakni 'hutan'. Builder disini cuma memain peranan alat pertama. Dengan hasil yang masih 'hidup', Basic Statistics diaktifkan. Kini QGIS pintar dan menanda 'Use only selected features'. Modul dikonfigur dan hasil adalah seperti dicari iaitu SUM=2185.01. Pada ujian kedua, carian asal disimpan sebagai lapisan 'hutan' lalu Basic Statistics diaktifkan. Kali ini 'Use only selected features' tidak ditanda. Modul dikonfigur dan sekali lagi, hasil adalah sama iaitu SUM=2185.01. Sungguh mudah dan berkesan si modul Basic Statistic ni.

Basic Statistics

Have you wondered how to get the 'sum of' something from a map, say, the total area of all the jungle polygon features ('hutan' as in Malay language)? Well, if you think the answer is by way of SQL query, think again because the Search Query Builder will not give the actual answer you seek. Use the right tool for the right job, my car mechanic would say and here things like sum of, mean, median and mode belong to the world of statistics, thus, the right tool for this subject is the Basic Statistics module under Vector/Analysis tools. In my first test, I used the Search Query Builder to make a selection, namely, 'hutan'. Here the Builder only plays the role of initial tool. With the result still live, activate Basic Statistics. QGIS was intelligent enough to tick 'Use only selected features'. I configured the module and got the answer I needed i.e. SUM=2185.01. In the second test, the earlier selection was saved as a layer called 'hutan' then Basic Statistics was activated. This time, 'Use only selected features' did not get ticked. Configuring the module, I got the same answer I sought i.e. SUM=2185.01. Simple and effective tool this Basic Statistic module.

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