Question: How many geolocated tweets do the authors analyze?
Evidence: The recent increase in digitally available language corpora made it possible to extend the traditional linguistic tools to a vast amount of often user-generated texts. Understanding how these corpora differ from traditional texts is crucial in developing computational methods for web search, information retrieval or machine translation BIBREF0 . The amount of these texts enables the analysis of language on a previously unprecedented scale BIBREF1 , BIBREF2 , BIBREF3 , including the dynamics, geography and time scale of language change BIBREF4 , BIBREF5 , social media cursing habits BIBREF6 , BIBREF7 , BIBREF8 or dialectal variations BIBREF9 .
From online user activity and content, it is often possible to infer different socio-economic variables on various aggregation scales. Ranging from showing correlation between the main language features on Twitter and several demographic variables BIBREF10 , through predicting heart-disease rates of an area based on its language use BIBREF11 or relating unemployment to social media content and activity BIBREF12 , BIBREF13 , BIBREF14 to forecasting stock market moves from search semantics BIBREF15 , many studies have attempted to connect online media language and metadata to real-world outcomes. Various studies have analyzed spatial variation in the text of OSN messages and its applicability to several different questions, including user localization based on the content of their posts BIBREF16 , BIBREF17 , empirical analysis of the geographic diffusion of novel words, phrases, trends and topics of interest BIBREF18 , BIBREF19 , measuring public mood BIBREF20 .
While many of the above cited studies exploit the fact that language use or social media activity varies in space, it is hard to capture the impact of the geographic environment on the used words or concepts. There is a growing literature on how the sheer size of a settlement influences the number of patents, GDP or the total road length driven by universal laws BIBREF21 . These observations led to the establishment of the theory of urban scaling BIBREF22 , BIBREF23 , BIBREF24 , BIBREF25 , BIBREF26 , BIBREF27 , BIBREF28 , BIBREF29 , BIBREF30 , where scaling laws with city size have been observed in various measures such as economic productivity BIBREF31 , human interactions BIBREF32 , urban economic diversification BIBREF33 , election data BIBREF34 , building heights BIBREF35 , crime concentration BIBREF36 , BIBREF37 or touristic attractiveness BIBREF38 .
In our paper, we aim to capture the effect of city size on language use via individual urban scaling laws of words. By examining the so-called scaling exponents, we are able to connect geographical size effects to systematic variations in word use frequencies. We show that the sensitivity of words to population size is also reflected in their meaning. We also investigate how social media language and city size affects the parameters of Zipf's law BIBREF39 , and how the exponent of Zipf's law is different from that of the literature value BIBREF39 , BIBREF40 . We also show that the number of new words needed in longer texts, the Heaps law BIBREF1 exhibits a power-law form on Twitter, indicating a decelerating growth of distinct tokens with city size.
In this study, we analyze 456 millions of these geolocated tweets collected between February 2012 and August 2014 from the area of the United States.
Answer: 456 millions.